Kezar Life Sciences (KZR) 424B5 Prospectus supplement for primary offering

Filed Pursuant to Rule 424(b)(5)
Registration No.: 333-232542

PROSPECTUS SUPPLEMENT (To Prospectus dated July 11, 2019)

16,115,385 Shares of Common Stock

Pre-Funded Warrants to Purchase 2,884,615 Shares of Common Stock

We are offering 16,115,385 shares of our common stock and, to certain investors in lieu thereof,pre-funded warrants to purchase 2,884,615 shares of our common stock, or thePre-Funded Warrants.

The purchase price of eachPre-Funded Warrant equals the public offering price per share of common stock, minus $0.001, and the exercise price of eachPre-Funded Warrant equals $0.001 per share. ThePre-Funded Warrants are exercisable at any time, provided that eachPre-Funded Warrant holder will be prohibited from exercising suchPre-Funded Warrants into shares of our common stock if, as a result of such exercise, the holder, together with its affiliates, would own more than 9.99% of the total number of shares of our common stock then issued and outstanding, which percentage may change at the holders’ election to any other number less than or equal to 19.99% upon 61 days’ notice to us. This prospectus supplement also relates to the offering of the shares of common stock issuable upon exercise of suchPre-Funded Warrants.

Our common stock is listed for trading on The Nasdaq Global Select Market under the symbol “KZR.” On January 30, 2020, the last reported sale price of our common stock was $2.77 per share. There is no established public market for thePre-Funded Warrants, and we do not intend to list thePre-Funded Warrants on The Nasdaq Global Select Market, any other national securities exchange or any other nationally recognized trading system.

We are an “emerging growth company” under applicable Securities and Exchange Commission rules and will be subject to reduced public company reporting requirements for this prospectus and future filings.

Our business and an investment in our securities involve significant risks. These risks are described under the caption “Risk Factors” beginning on pageS-11 of this prospectus supplement and in the documents incorporated by reference into this prospectus supplement and the accompanying prospectus.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or passed upon the accuracy or adequacy of this prospectus supplement and the accompanying prospectus. Any representation to the contrary is a criminal offense.

	Per Share		Per Pre-Funded Warrant		Total
Public offering price	$	2.60	$	2.599	$	49,397,115
Underwriting discounts and commissions(1)	$	0.156	$	0.156	$	2,963,827
Proceeds, before expenses, to us	$	2.444	$	2.443	$	46,433,288

(1) See “Underwriting” for a description of compensation payable to the underwriters.

The underwriters may also purchase up to 2,850,000 additional shares of our common stock from us at the public offering price, less the underwriting discounts and commissions, within 30 days from the date of this prospectus supplement.

Entities affiliated with Morningside Venture Investments Ltd., or Morningside, our existing stockholder, and certain of our directors and officers have indicated an interest to purchase up to an aggregate of $30.3 million of the securities offered hereby. However, because these indications of interest are not binding agreements or commitments to purchase, such stockholders or their affiliates may elect to purchase fewer securities or not purchase any securities in this offering. In addition, the underwriters may determine to sell more, fewer or no securities in this offering to such stockholders or their affiliates.

The underwriters expect to deliver the securities against payment in New York, New York on February 4, 2020.

Joint Book-Running Managers

Cowen Wells Fargo Securities William Blair

January 31, 2020.

TABLE OF CONTENTS

Prospectus Supplement

ABOUT THIS PROSPECTUS SUPPLEMENT	S-ii
PROSPECTUS SUPPLEMENT SUMMARY	S-1
RISK FACTORS	S-11
SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTS	S-13
USE OF PROCEEDS	S-15
DILUTION	S-16
DESCRIPTION OFPRE-FUNDED WARRANTS	S-18
MATERIAL U.S. FEDERAL INCOME TAX CONSEQUENCES	S-20
UNDERWRITING	S-27
LEGAL MATTERS	S-32
EXPERTS	S-32
WHERE YOU CAN FIND MORE INFORMATION	S-32
INCORPORATION OF CERTAIN INFORMATION BY REFERENCE	S-33

Prospectus

ABOUT THIS PROSPECTUS	ii
SUMMARY	1
RISK FACTORS	10
SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTS	11
USE OF PROCEEDS	13
DESCRIPTION OF CAPITAL STOCK	14
DESCRIPTION OF DEBT SECURITIES	20
DESCRIPTION OF WARRANTS	27
LEGAL OWNERSHIP OF SECURITIES	29
PLAN OF DISTRIBUTION	33
LEGAL MATTERS	35
EXPERTS	35
WHERE YOU CAN FIND MORE INFORMATION	36
INCORPORATION OF CERTAIN INFORMATION BY REFERENCE	36

ABOUT THIS PROSPECTUS SUPPLEMENT

This document is part of a “shelf” registration statement on FormS-3 that we filed with the Securities and Exchange Commission, or the SEC, and is in two parts. The first part is this prospectus supplement, which describes the specific terms of this offering and also adds to and updates information contained in the accompanying prospectus and the documents incorporated by reference herein. The second part, the accompanying prospectus, provides more general information. Generally, when we refer to this prospectus, we are referring to both parts of this document combined. To the extent there is a conflict between the information contained in this prospectus supplement and the information contained in the accompanying prospectus or any document incorporated by reference therein filed prior to the date of this prospectus supplement, you should rely on the information in this prospectus supplement; provided that if any statement in one of these documents is inconsistent with a statement in another document having a later date—for example, a document incorporated by reference in the accompanying prospectus—the statement in the document having the later date modifies or supersedes the earlier statement.

We further note that the representations, warranties and covenants made by us in any agreement that is filed as an exhibit to any document that is incorporated by reference herein were made solely for the benefit of the parties to such agreement, including, in some cases, for the purpose of allocating risk among the parties to such agreements, and should not be deemed to be a representation, warranty or covenant to you. Moreover, such representations, warranties or covenants were accurate only as of the date when made. Accordingly, such representations, warranties and covenants should not be relied on as accurately representing the current state of our affairs.

Neither we nor the underwriters have authorized any person to provide any information or to make any representation other than those contained or incorporated by reference in this prospectus supplement or in the accompanying prospectus. We take no responsibility for, and can provide no assurance as to the reliability of, any other information that others may give you. This prospectus supplement and the accompanying prospectus do not constitute an offer to sell or the solicitation of an offer to purchase the securities offered by this prospectus supplement and the accompanying prospectus in any jurisdiction to or from any person to whom or from whom it is unlawful to make such offer or solicitation of an offer in such jurisdiction.

The information contained in this prospectus supplement or the accompanying prospectus, or incorporated by reference herein or therein is accurate only as of the respective dates thereof, regardless of the time of delivery of this prospectus supplement and the accompanying prospectus or of any sale of our securities. It is important for you to read and consider all information contained in this prospectus supplement and the accompanying prospectus, including the documents incorporated by reference herein and therein, in making your investment decision. You should also read and consider the information in the documents to which we have referred you in the sections entitled “Where You Can Find More Information” and “Incorporation of Certain Information by Reference” in this prospectus supplement and in the accompanying prospectus.

We are offering to sell, and seeking offers to buy, our securities only in jurisdictions where offers and sales are permitted. The distribution of this prospectus supplement and the accompanying prospectus and this offering in certain jurisdictions may be restricted by law. Persons outside the United States who come into possession of this prospectus supplement and the accompanying prospectus must inform themselves about, and observe any restrictions relating to, this offering and the distribution of this prospectus supplement and the accompanying prospectus outside the United States. This prospectus supplement and the accompanying prospectus do not constitute, and may not be used in connection with, an offer to sell, or a solicitation of an offer to buy, any securities offered by

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this prospectus supplement and the accompanying prospectus by any person in any jurisdiction in which it is unlawful for such person to make such an offer or solicitation.

Unless the context indicates otherwise, references in this prospectus to “Kezar,” “the Company,” “we,” “us,” “our” and similar references refer to Kezar Life Sciences, Inc. and its wholly owned Australian subsidiary, Kezar Life Sciences Australia Pty Ltd.

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PROSPECTUS SUPPLEMENT SUMMARY

This summary highlights selected information contained elsewhere in this prospectus supplement and the accompanying prospectus and in the documents we incorporate by reference. This summary does not contain all of the information you should consider before investing in our securities. You should read this entire prospectus supplement and the accompanying prospectus carefully, especially the risks of investing in our securities discussed under the section titled “Risk Factors” in this prospectus supplement and under similar headings in our Annual Report on Form10-K for the year ended December 31, 2018 and in our Quarterly Report on Form10-Q for the quarter ended September 30, 2019, which are incorporated by reference in this prospectus supplement, along with our consolidated financial statements and notes to those consolidated financial statements and the other information incorporated by reference in this prospectus supplement and the accompanying prospectus, before making an investment decision.

Company Overview

We are a clinical-stage biotechnology company, discovering and developing novel small molecule therapeutics to treat unmet needs in autoimmunity and cancer. Our lead product candidate,KZR-616, afirst-in-class selective immunoproteasome inhibitor, has completed testing in healthy volunteers, and we are now enrolling patients in both phases of the MISSION trial, a Phase 1b/2 clinical trial in systemic lupus erythematosus, also known as lupus or SLE, and lupus nephritis. We believe that the immunoproteasome is a validated target for the treatment of a wide variety of autoimmune diseases given the compelling published activity seen withnon-selective proteasome inhibitors administered to patients with severe autoimmune diseases. Based on results from our Phase 1a studies in healthy volunteers and the preliminary results from the Phase 1b portion of the MISSION trial,KZR-616 has largely avoided adverse effects associated with currently marketednon-selective proteasome inhibitors, as exhibited in clinical studies conducted by third parties, including side effects which we believe prevent them from being utilized as a chronic treatment in autoimmune disorders. We intend to developKZR-616 to address underserved autoimmune diseases. The Phase 2 portion of the MISSION trial is evaluatingKZR-616 for the treatment of lupus nephritis, for which there are currently no drugs approved by the Food and Drug Administration, or FDA. We are also leveraging the broad therapeutic potential ofKZR-616 to develop the product candidate in four additional autoimmune indications: dermatomyositis, or DM, polymyositis, or PM, autoimmune hemolytic anemia, or AIHA, and immune thrombocytopenia, or ITP.

Additionally, we are advancing our novel research platform targeting the Sec61 translocon and the protein secretion pathway to discover and develop small molecule therapeutics targeting oncology indications. We believe this discovery platform has the potential to yield oral small molecule candidates that, if successfully developed and approved, could serve as alternatives to currently marketed biologic therapeutics to act as cytotoxic anti-cancer agents or to block the secretion of novel targets of interest in immuno-oncology or inflammation. Our first clinical candidate in this program,KZR-261, has demonstrated broad anti-tumor activity in preclinical models of both solid and hematologic malignancies.KZR-261 is undergoing laboratory studies and manufacturing activities in support of an investigational new drug, or IND, application, which we anticipate submitting to the FDA in the first quarter of 2021 for a Phase 1 clinical trial in solid tumors.

KZR-616: Selective Immunoproteasome Inhibitor

We believe thatKZR-616 has potential to be developed for the treatment of multiple autoimmune disease indications. In the last decade, research directed by our Chief Scientific Officer, along with work performed in multiple academic laboratories, has led to over 15 peer-reviewed publications

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showing that selective immunoproteasome inhibition resulted in a broad anti-inflammatory response, reducing autoimmune disease in animal models of lupus, lupus nephritis, rheumatoid arthritis, inflammatory bowel disease, multiple sclerosis, Type 1 diabetes and other indications. This immunomodulatory response was broadly seen across many cell types of the immune system, including both T cells and B cells, and was demonstrated in a safe andnon-immunosuppressive manner. This is distinct from other agents currently used to treat autoimmunity, which typically target a single cytokine or immune cell type or are broadly immunosuppressive.

Autoimmunity and Selective Inhibition of the Immunoproteasome

Autoimmune disease is an immune response directed against the body’s own healthy cells and tissues. Approximately 50 million people in the United States suffer from more than 100 diagnosed autoimmune diseases according to the American Autoimmune Related Diseases Association, Inc. In indications large and small, there remain significant unmet medical needs and indications with no approved drugs beyond broadly prescribed corticosteroids and similar immunosuppressive regimens. These result in increased risk of infection and malignancy and a wide variety of side effects. In diseases such as lupus nephritis, these regimens do not induce high rates of clinically meaningful responses.

Found in all cells of the body, proteasomes regulate intracellular protein degradation and are essential for many cellular processes such as cell division, cell differentiation and cytokine production. There are two main forms of the proteasome: the constitutive proteasome and the immunoproteasome. In most tissues of the body, the constitutive proteasome is the predominant form. In cells of the immune system, the immunoproteasome is the predominant form. While both forms of the proteasome mediate protein degradation, the two forms of the proteasome accomplish this utilizing different active sites. These active sites are responsible for cleaving and degrading proteins. Selective inhibition of the immunoproteasome has the potential to reduce inflammation by targeting dysfunctional immune cells involved in autoimmunity, such as T cells and B cells, without causing widespread immunosuppression.

Safety and Efficacy of Approved Proteasome Inhibitors

The three proteasome inhibitors approved for the treatment of multiple myeloma, Velcade^® (bortezomib), Kyprolis^® (carfilzomib) and Ninlaro^® (ixazomib), are potent “dual inhibitors” of both the immunoproteasome and the constitutive proteasome. This dual-targeting profile is necessary to make them effective treatments for multiple myeloma. However, dual proteasome inhibition is associated with hematologic issues such as thrombocytopenia, neutropenia and anemia, as well as constitutional toxicities such as fatigue and myalgia. In addition, Velcade and Ninlaro are associated with risk of peripheral neuropathy, likely due to theoff-target activity of these drugs against proteins found in peripheral neurons.

Velcade has demonstrated clinical activity in several autoimmune diseases, including lupus, lupus nephritis, rheumatoid arthritis, immune thrombocytopenia, autoimmune hemolytic anemia, primary Sjögren’s syndrome and graft-versus-host disease. In preclinical models, proteasome inhibition with Velcade blocked production of most inflammatory cytokines, including many of those targeted by current biologic drugs. However, long-term, chronic administration of Velcade in the setting of autoimmune diseases is not considered feasible due to its side effect profile, in particular hematologic toxicities and risk of peripheral neuropathy. As a result, we believe that this promising drug target has remained untapped for use in the chronic treatment of autoimmune diseases.

We believe we are the only company with a selective immunoproteasome inhibitor that is in clinical trials for the treatment of autoimmune disorders. In addition, we believe thatKZR-616, if successfully

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developed and approved, may have the ability to become the standard of care across a broad range of autoimmune diseases based on the following expected key attributes:

∎ broad immunomodulatory activity that may allow it to outperform approved therapies and to work in indications where other drugs have failed;

∎ low infection rates observed in clinical trials to date, which indicates a potential lack of immunosuppression, a key drawback to other approved therapies in autoimmunity; and

∎ avoidance of systemic toxicities associated with dual proteasome inhibitors and the peripheral neuropathy associated with Velcade and Ninlaro.

Clinical Development ofKZR-616

We are focusing our initial development ofKZR-616 in severe orphan autoimmune diseases where limited treatment options exist. Currently, there are no approved treatments for lupus nephritis or AIHA in the United States or Europe, and there are limited approved treatments for DM, PM, and ITP in the United States and Europe. We estimate the addressable patient population in the United States for lupus, lupus nephritis, DM/PM and AIHA/ITP to be 460,000, 100,000 to 200,000, 70,000 and 140,000, respectively.

We have opened three Phase 2 trials across five separate autoimmune diseases of high unmet need: the MISSION trial in patients with lupus nephritis; the PRESIDO trial in patients with DM and PM; and the MARINA trial in patients with AIHA and ITP.

Phase 2 Clinical Trials

The Phase 2 portion of MISSION is a randomized, placebo-controlled, double-blind trial to evaluate the safety and efficacy ofKZR-616 in patients with active proliferative lupus nephritis. The primary endpoints of this portion of the MISSION trial are safety and tolerability. Secondary and exploratory endpoints include pharmacokinetics, or PK, pharmacodynamics, or PD, biomarker assessments and additional measures of efficacy. This trial includes four treatment arms evaluatingKZR-616 administered subcutaneously once weekly for 24 weeks at dose levels of 30 mg, 45 mg and 60 mg, compared to placebo. We expect to enroll 64 patients.

PRESIDIO is a Phase 2 randomized, placebo-controlled, double-blind, crossover, multicenter trial to evaluate the safety, tolerability, efficacy, PK and PD ofKZR-616 in patients with active PM or DM. During the32-week treatment period, patients receive either 45 mg ofKZR-616 or placebo subcutaneously once weekly for 16 weeks followed by a crossover to the other treatment arm for an additional 16 weeks. We expect to enroll 24 patients in the trial. We believe thatKZR-616 has the potential to be developed into a treatment for patients with DM and PM, which isin-part supported by preclinical data in a mouse model of PM and DM that demonstrated immunoproteasome inhibition and improved muscle function.

MARINA is a Phase 2 randomized, dose-blind, multicenter trial designed to evaluate the safety, tolerability, efficacy, PK and PD ofKZR-616 in patients with active AIHA or ITP. Patients with AIHA or ITP will be randomized to receive either 30 mg or 45 mg ofKZR-616 subcutaneously once weekly for 13 weeks, followed by 12 weeks offollow-up. We expect to enroll 40 patients in the trial. We believe that whole blood RNASeq data from MISSION, which showed a decrease in multiple inflammatory gene signature and prolonged increase in erythropoietic gene signatures in SLE patients, support the broad potential anti-inflammatory activity ofKZR-616 and an application in patients with AIHA.

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Phase 1 Clinical Trials

We have conducted and presented at medical conferences the results of two Phase 1a studies evaluatingKZR-616 in healthy volunteers. Results from these studies, involving administration of two different formulations ofKZR-616 to a total of 100 healthy volunteers, demonstrated thatKZR-616 was well tolerated in up to 75 mg (the highest tested dose). We believe that these results support development ofKZR-616 in autoimmune disorders based on the following observations:

∎ consistent and reproducible pharmacology;

∎ a distinct safety profile from dual proteasome inhibitors as a class; and

∎ an encouraging safety and tolerability profile.

The Phase 1b portion of MISSION is an open-label, dose escalation and dose-finding study in patients with active lupus with or without lupus nephritis who have received at least one standard therapeutic regimen. Patients receive 13 weeks of weekly subcutaneous treatment, followed by 12 weeks offollow-up. Preliminary data generated from the Phase 1b portion of the MISSION trial, almost exclusively in SLE patients, continues to support the advancement ofKZR-616 into Phase 2 trials across multiple autoimmune indications. As of the September 2019 data cutoff, the Phase 1b portion of MISSION enrolled 32 patients across four cohorts. Results presented at both the European League Against Rheumatism (EULAR) and American College of Rheumatology (ACR) Conferences in 2019 showed thatKZR-616:

∎ was well tolerated for 13 weeks of treatment;

∎ largely avoided toxicities seen with dual proteasome inhibitors in third-party clinical trials;

∎ exhibited low rates of infection (which suggest immunomodulatory activity without inducing immunosuppressive side effects);

∎ induced broad improvement across seven measured parameters of disease activity across organ systems;

∎ showed a broad anti-inflammatory gene expression response as evidenced by whole blood RNASeq data;

∎ demonstrated consistent, dose proportional PK; and

∎ reached target levels of immunoproteasome inhibition with all dose levels.

Broad and consistent improvements were seen across multiple measures and assessments of disease activity. Of the 16 patients completing 13 weeks of treatment:

∎ 94% had a numerical improvement on at least four measured parameters or assessments of disease activity;

∎ 75% had at least atwo-point decrease in Systemic Lupus Erythematosus Disease Activity Index 2000, or SLEDAI;

∎ 67% had at least a four-point decrease in Cutaneous Lupus Erythematosus Severity Index-Activity, orCLASI-A (where baseline was at least four); and

∎ 56% had at least a 50% improvement in tender joint counts and swollen joint counts.

Additionally, Physician Global Assessment, Patient Global Assessment, and Patient Assessment of Pain were reduced by at least ten points in 50%, 75% and 69% of the 16 patients who completed 13 weeks of treatment, respectively.Step-up dosing to 60 mg exhibited improved tolerability, such that nausea and vomiting were reported in less than 20% of patients, and discontinuation rates declined from 38% to 20% compared to the cohort receiving an initial dose of 60 mg.

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A single patient with active proliferative lupus nephritis, who completed the trial following the last data cutoff, was enrolled in the Phase 1b portion of the study and was treated at 45 mg after initial doses of 30 mg. The patient is a29-year old Asian female who was diagnosed with lupus nephritis in 2015. She entered the study with a positive antinuclear antibody test, low complement levels, proliferative lupus nephritis, a near-nephrotic range of proteinuria with a 3.85 mg/mg urine protein to creatinine ratio, or UPCR, and a baseline SLEDAI score of 17, indicative of severe disease. The UPCR dropped to 0.6 mg/mg at week 17 (four weeks after the last dose ofKZR-616), and the SLEDAI score dropped to 8 at week 13, which was maintained through thefollow-up period to week 25. The investigator believes that the unexpected drop and maintenance in UPCR was probably due toKZR-616. The patient also experienced one serious adverse event after the first dose of 30 mg, which was related to a first dose effect of fever, thus she was maintained at 45 mg until the end of her treatment.

We caution that these data from the Phase 1b portion of the MISSION trial are preliminary, particularly with respect to the single patient described above, and will require confirmation in additional patients as well aslonger follow-up to draw any clinical conclusion. In addition, these preliminary data should not be viewed as an indication, belief or guarantee that other patients enrolled in the MISSION trial will achieve similar results or that the preliminary results from this patient will be maintained. For more information about the risks of preliminary clinical data, including the risk that the preliminary data from this single patient enrolled in the MISSION trial to date may not be maintained or replicated in that patient or in any other enrolled patients, see “Risk Factors—Risks Related to the Development and Commercialization of Our Product Candidates—Interimtop-line and preliminary data from our clinical trials that we announce or publish from time to time may change as more patient data become available and are subject to audit and verification procedures that could result in material changes in the final data” in this prospectus supplement.

Protein Secretion and the Sec61 Translocon

We are conducting research and discovery efforts targeting protein secretion pathways as potential therapies for oncology and immuno-oncology indications. We believe that targeting this pathway has the potential to inhibit multiple therapeutically relevant targets with a single small molecule.

In mammalian cells, the secretion of proteins such as cytokines and the expression of cell surface transmembrane proteins such as cytokine receptors involve a process called cotranslational translocation. For nearly all secreted and transmembrane proteins (approximately 5,000 to 7,000 proteins), this process occurs via the Sec61 translocon, a highly conserved multi-subunit protein complex found in the membrane of the endoplasmic reticulum of all cells. Inhibition of the Sec61 translocon with small molecules blocks the secretion of some or all proteins, which can result in several physiologic outcomes, including altered cellular function, inhibition of cytokine release and/or cell death. Our scientists have been researching the protein secretion pathway and ways to therapeutically target this key aspect of cellular function for more than five years. We have developed several novel experimental platforms to study small molecule inhibitors of Sec61, which can result in several physiologic outcomes, including altered cellular function, inhibition of cytokine release and/or cell death. We believe this platform has the potential to yield small molecule alternatives to currently marketed biologic therapeutics to act as cytotoxic anti-cancer agents or to block the secretion of novel targets of interest in inflammation or immuno-oncology.

In December 2019, we highlighted our work from the protein secretion platform during the 61^st American Society of Hematology (ASH) Annual Meeting. Our preclinical research on the Sec61 transolocon demonstrated high degrees of potency against a large number of therapeutically relevant oncology and immuno-oncology targets that are Sec61 client proteins, translating into broad anti-tumor

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activity. Our discovery-stage Sec61 inhibitors have shown to induce anti-tumor activity against multiple hematologic tumor types without inducing cell death in normal cells or significant toxicity in animals. Genomic and proteomic analysis reveal a proteotoxic stress response as a potential biomarker for sensitivity across multiple tumor types, and we have observed synergy with proteasome inhibitors in multiple myeloma models.

KZR-261

KZR-261, a novel,first-in-class protein secretion inhibitor, is the first clinical candidate to be nominated from our research and discovery efforts targeting protein secretion pathways.KZR-261 is a broad-spectrum, anti-tumor agent that acts through direct interaction and inhibition of Sec61 activity. The compound was discovered at Kezar through a medicinal chemistry campaign in which several scaffolds were progressed through our proprietary workflow of protein secretion assays. As a result, we have established a unique and broad library of protein secretion inhibitors and a strong patent position aroundKZR-261 and its analogs. We have observed encouraging data withKZR-261 that exhibit its potential to be a new anti-cancer agent for the treatment of solid and hematologic malignancies. It has been shown to induce simultaneous inhibition of multiple, clinically relevant proteins including oncogenic drivers, angiogenic factors and immune checkpoints. The preclinical data generated withKZR-261 increases our confidence that inhibiting the Sec61 translocon may treat a variety of solid and hematologic tumor types.IND-enabling studies are currently underway, and we expect to file an IND application for the treatment of solid tumors in the first quarter of 2021.

Our Pipeline

The following table sets forth the status and initial focus of our lead product candidate and protein secretion program:

Financial Update

As of December 31, 2019, we had approximately $78 million of cash, cash equivalents and marketable securities and 19.2 million shares of common stock outstanding. These preliminary estimates are not a comprehensive statement of our financial results for the year ended December 31, 2019 and have not been audited, reviewed, or compiled by our independent registered public accounting firm. Our actual consolidated cash, cash equivalents and marketable securities balance

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and shares of common stock outstanding as of December 31, 2019 may differ from these estimates due to the completion of ouryear-end closing and auditing procedures. Our audited consolidated financial statements for the year ended December 31, 2019 will not be available until after this offering is completed, and consequently will not be available to you prior to investing in this offering.

Corporate Information

We were incorporated under the laws of the State of Delaware on February 19, 2015. Our principal executive offices are located at 4000 Shoreline Court, Suite 300, South San Francisco, California 94080, and our telephone number is (650)822-5600. In January 2016, we incorporated our wholly owned Australian subsidiary, Kezar Life Sciences Australia Pty Ltd, which is a proprietary company limited by shares. Our corporate website address iswww.kezarlifesciences.com. Information contained on, or accessible through, our website is not a part of this prospectus supplement or the accompanying prospectus and will not be deemed to be incorporated by reference herein or therein. We have included our website in this prospectus supplement solely as an inactive textual reference.

“Kezar,” the Kezar logo and other trademarks, trade names or service marks of Kezar Life Sciences, Inc. appearing in this prospectus supplement and the accompanying prospectus are the property of Kezar Life Sciences, Inc. All other trademarks, trade names and service marks appearing in this prospectus supplement and the accompanying prospectus are the property of their respective owners. Solely for convenience, the trademarks and trade names in this prospectus supplement and the accompanying prospectus may be referred to without the^® and^™ symbols, but such references should not be construed as any indicator that their respective owners will not assert their rights thereto.

Implications of Being an Emerging Growth Company and a Smaller Reporting Company

We are an “emerging growth company” as defined in the Jumpstart Our Business Startups Act of 2012, or the JOBS Act. For so long as we remain an emerging growth company, we are permitted and intend to take advantage of specified reduced reporting and other burdens that are otherwise applicable generally to public companies, including:

∎ being permitted to provide only two years of audited financial statements, in addition to any required unaudited interim financial statements, with correspondingly reduced “Management’s Discussion and Analysis of Financial Condition and Results of Operations” disclosure;

∎ not being required to comply with the auditor attestation requirements in the assessment of our internal control over financial reporting;

∎ not being required to comply with any requirement that may be adopted by the Public Company Accounting Oversight Board regarding mandatory audit firm rotation or a supplement to the auditor’s report providing additional information about the audit and the financial statements;

∎ reduced disclosure obligations regarding executive compensation in our periodic reports, proxy statements and registration statements; and

∎ not being required to hold a nonbinding advisory vote on executive compensation and stockholder approval of any golden parachute payments not previously approved.

We may take advantage of these reporting exemptions until we are no longer an emerging growth company. We will remain an emerging growth company until the earlier of: (i) December 31, 2023; (ii) the last day of the fiscal year in which we have total annual gross revenue of at least $1.07 billion; (iii) the last day of the fiscal year in which we are deemed to be a large accelerated filer, which means the market value of our common stock held bynon-affiliates exceeds $700 million as of June 30 ofsuch fiscal year; or (iv) the date on which we have issued more than $1.0 billion innon-convertible debt

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during the prior three-year period. We may choose to take advantage of some or all of these available exemptions. We have taken advantage of some reduced reporting requirements in our public filings. Accordingly, the information that we provide stockholders may be different than the information you receive from other public companies in which you hold stock.

In addition, the JOBS Act provides that an emerging growth company can take advantage of an extended transition period for complying with new or revised accounting standards. This provision allows an emerging growth company to delay the adoption of some accounting standards until those standards would otherwise apply to private companies. We have irrevocably elected not to avail ourselves of delayed adoption of new or revised accounting standards and, therefore, we will be subject to the same requirements to adopt new or revised accounting standards as other public companies that are not emerging growth companies.

We are also a smaller reporting company as defined in the Securities Exchange Act of 1934, as amended, or the Exchange Act. We may continue to be a smaller reporting company even after we are no longer an emerging growth company. We may take advantage of certain of the scaled disclosures available to smaller reporting companies and will be able to take advantage of these scaled disclosures for so long as (i) the market value of our voting andnon-voting common stock held bynon-affiliates is less than $250.0 million measured on the last business day of our second fiscal quarter or (ii) our annual revenue is less than $100.0 million during the most recently completed fiscal year and the market value of our voting andnon-voting common stock held bynon-affiliates is less than $700.0 million measured on the last business day of our second fiscal quarter.

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THE OFFERING

Common stock offered by us 16,115,385 shares

Pre-Funded Warrants offered by us In lieu of shares of common stock, we are offering to certain purchasersPre-Funded Warrants to purchase 2,884,615 shares of common stock. The purchase price of eachPre-Funded Warrant will equal the public offering price per share of common stock, minus $0.001, and the exercise price of eachPre-Funded Warrant will be $0.001 per share. EachPre-Funded Warrant will be exercisable upon issuance. This prospectus supplement also relates to the offering of the shares of common stock issuable upon exercise of suchPre-Funded Warrants.

There is currently no market for thePre-Funded Warrants and none is expected to develop after this offering. We do not intend to list thePre-Funded Warrants on The Nasdaq Stock Market, any other national securities exchange or other nationally recognized trading system. See “Description ofPre-FundedWarrants—Pre-Funded Warrants” for additional information.

Option to purchase additional shares from us We have granted the underwriters an option for a period of 30 days to purchase up to 2,850,000 additional shares of our common stock from us at the public offering price, less the underwriting discounts and commissions. The number of shares subject to the underwriters’ option will equal 15% of the total number of shares of common stock we are offering plus the shares underlying thePre-Funded Warrants.

Common stock to be outstanding immediately following this offering 35,257,030 shares, or 38,107,030 shares if the underwriters’ option to purchase additional shares from us is exercised in full (in each case excluding any shares of common stock issuable upon the exercise of thePre-Funded Warrants)

Use of proceeds We intend to use the net proceeds from this offering primarily to fund the research and development of our product candidates, acquire or license products or technologies that are complementary to our own, although we have no current plans, commitments or agreements with respect to any acquisitions or

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licenses as of the date of this prospectus supplement, and for working capital and general corporate purposes. See “Use of Proceeds.”

Risk factors Investing in our securities involves significant risks. See “Risk Factors” on pageS-11of this prospectus supplement and under similar headings in other documents incorporated by reference herein.

Nasdaq Global Select Market symbol “KZR”

Entities affiliated with Morningside, our existing stockholder, and certain of our directors and officers have indicated an interest to purchase up to an aggregate of $30.3 million of the securities offered hereby. However, because these indications of interest are not binding agreements or commitments to purchase, such stockholders or their affiliates may elect to purchase fewer securities or not purchase any securities in this offering. In addition, the underwriters may determine to sell more, fewer or no securities in this offering to such stockholders or their affiliates.

The number of shares of our common stock to be outstanding immediately after this offering is based on 19,141,645 shares of our common stock outstanding as of September 30, 2019, and excludes:

∎ 3,348,044 shares of our common stock issuable upon the exercise of outstanding stock options as of September 30, 2019 at a weighted average exercise price of $7.39 per share;

∎ 1,574,288 shares of our common stock reserved for future issuance under our 2018 Equity Incentive Plan, or the 2018 Plan, as of September 30, 2019, as well as any future increases in the number of shares of common stock reserved for issuance under our 2018 Plan;

∎ 380,920 shares of our common stock reserved for future issuance under our 2018 Employee Stock Purchase Plan, or ESPP, as of September 30, 2019, as well as any future increases in the number of shares of common stock reserved for issuance under our ESPP; and

∎ 2,884,615 shares of our common stock underlying thePre-Funded Warrants being offered hereby.

Except as otherwise indicated, the information in this prospectus supplement assumes no exercise of the outstanding stock options or thePre-Funded Warrants and no exercise by the underwriters of their option to purchase additional shares.

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RISK FACTORS

An investment in our securities involves a high degree of risk. Before deciding whether to invest in our securities, you should carefully consider the risks described below and those discussed under the section titled “Risk Factors” contained in our Annual Report on Form10-K for the year ended December 31, 2018 and in our Quarterly Report on Form10-Q for the quarter ended September 30, 2019, which are incorporated by reference in this prospectus supplement and the accompanying prospectus, together with other information in this prospectus supplement, the accompanying prospectus, the information and documents incorporated by reference herein and therein, and in any free writing prospectus that we have authorized for use in connection with this offering. If any of these risks actually occurs, our business, financial condition, results of operations or cash flow could be seriously harmed. This could cause the trading price of our securities to decline, resulting in a loss of all or part of your investment.

Risks Related to the Development and Commercialization of Our Product Candidates

Interimtop-line and preliminary data from our clinical trials that we announce or publish from time to time may change as more patient data become available and are subject to audit and verification procedures that could result in material changes in the final data.

From time to time, we may publish interimtop-line or preliminary data from our clinical trials. Interim data from clinical trials that we may complete are subject to the risk that one or more of the clinical outcomes may materially change as patient enrollment continues and more patient data become available. Preliminary ortop-line data also remain subject to audit and verification procedures that may result in the final data being materially different from the preliminary data we previously published. Preliminary ortop-line data may include, for example, data regarding a small percentage of the patients enrolled in a clinical trial, and such preliminary data should not be viewed as an indication, belief or guarantee that other patients enrolled in such clinical trial will achieve similar results or that the preliminary results from such patients will be maintained. As a result, interim and preliminary data should be viewed with caution until the final data are available. Differences between preliminary or interim data and final data could significantly harm our business prospects and may cause the trading price of our common stock to fluctuate significantly.

Risks Related to this Offering

Our management will have broad discretion as to the use of the net proceeds from this offering and might apply the net proceeds from this offering in ways with which you do not agree and in ways that may impair the value of your investment.

We intend to use the net proceeds from this offering primarily to fund the research and development of our product candidates, acquire or license products or technologies that are complementary to our own, although we have no current plans, commitments or agreements with respect to any acquisitions or licenses as of the date of this prospectus supplement, and for working capital and general corporate purposes. Pending the use of net proceeds in this offering, we intend to invest the net proceeds in a variety of capital preservation instruments, including short-term, interest-bearing obligations, investment-grade instruments, certificates of deposit or direct or guaranteed obligations of the United States government. Our management has broad discretion as to the use of these proceeds and you will be relying on the judgment of our management regarding the application of these proceeds. We might apply these proceeds in ways with which you do not agree, or in ways that do not yield a favorable return. If our management applies these proceeds in a manner that does not yield a significant return, if any, on our investment of these net proceeds, it could compromise our ability to pursue our growth strategy and adversely affect the market price of our common stock.

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Concentration of ownership of our common stock among our existing executive officers, directors and principal stockholders may prevent new investors from influencing significant corporate decisions.

Based upon our shares of our common stock outstanding as of September 30, 2019, our executive officers, directors and stockholders who owned more than 5% of our outstanding common stock do, in the aggregate, beneficially own shares representing approximately 46% of our outstanding common stock.

Entities affiliated with Morningside, an existing stockholder, and certain of our directors and officers have indicated an interest to purchase up to an aggregate of $30.3 million of the securities offered hereby. The ownership percentage upon the completion of this offering noted above does not reflect the potential purchase of any securities in this offering by such stockholders. If these stockholders participate in this offering, the percentage noted above could potentially increase. These stockholders, acting together, will be able to significantly influence all matters requiring stockholder approval, including the election and removal of directors and any merger or other significant corporate transactions. The interests of this group of stockholders may not coincide with the interests of other stockholders.

There is no public market for thePre-Funded Warrants being offered in this offering.

There is no established public trading market for thePre-Funded Warrants being offered in this offering, and we do not expect a market to develop. In addition, we do not intend to apply to list these warrants on any securities exchange or nationally recognized trading system, including The Nasdaq Global Select Market. Without an active market, the liquidity of these warrants will be limited.

Holders ofPre-Funded Warrants purchased in this offering will have no rights as common stockholders until such holders exercise their warrants and acquire our common stock.

Until holders ofPre-Funded Warrants acquire shares of our common stock upon exercise of such warrants, the holders will have no rights with respect to the shares of our common stock underlying such warrants. Upon exercise of thePre-Funded Warrants, the holders will be entitled to exercise the rights of a common stockholder only as to matters for which the record date occurs after the exercise date.

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SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTS

This prospectus supplement, the accompanying prospectus, the documents incorporated by reference herein and therein and any free writing prospectus that we have authorized for use in connection with this offering contain forward-looking statements within the meaning of Section 27A of the Securities Act of 1933, as amended, or the Securities Act, and Section 21E of the Exchange Act. These statements are based on our management’s current beliefs, expectations and assumptions about future events, conditions and results and on information currently available to us. Discussions containing these forward-looking statements may be found, among other places, in the sections titled “Business,” “Risk Factors” and “Management’s Discussion and Analysis of Financial Condition and Results of Operations” incorporated by reference from our most recent Annual Report on Form10-K and most recent Quarterly Report on Form10-Q, as well as any amendments thereto, filed with the SEC.

In some cases, you can identify forward-looking statements by terminology such as “as “aim,” “anticipate,” “assume,” “believe,” “contemplate,” “continue,” “could,” “design,” “due,” “estimate,” “expect,” “goal,” “intend,” “may,” “objective,” “plan,” “predict,” “positioned,” “potential,” “seek,” “should,” “target,” “will,” “would” or the negative or plural of those terms, and similar expressions intended to identify statements about the future, although not all forward-looking statements contain these words. These forward-looking statements involve known and unknown risks, uncertainties and other factors that may cause our actual results, levels of activity, performance or achievements to be materially different from the information expressed or implied by these statements.

Any statements in this prospectus supplement, the accompanying prospectus, the documents incorporated by reference herein and therein and any free writing prospectus that we have authorized for use in connection with this offering about our expectations, beliefs, plans, objectives, assumptions or future events or performance are not historical facts and are forward-looking statements. Forward-looking statements may include, but are not limited to, statements regarding:

∎ our plans to develop and commercialize our product candidates;

∎ the initiation, timing, progress and expected results of our current and future clinical trials and our research and development programs;

∎ our estimates regarding expenses, future revenue, capital requirements and needs for additional financing;

∎ our ability to successfully acquire orin-license additional product candidates or other technology on reasonable terms;

∎ our ability to maintain and establish collaborations or strategic relationships or obtain additional funding;

∎ the timing and likelihood of obtaining regulatory approval of our current and future product candidates;

∎ our expectations regarding the potential market size and the rate and degree of market acceptance of such product candidates;

∎ our ability to fund our working capital requirements and expectations regarding the sufficiency of our capital resources;

∎ the implementation of our business model and strategic plans for our business and product candidates;

∎ the scope of protection we are able to establish and maintain for intellectual property rights and the duration of our patent rights covering our product candidates;

∎ developments or disputes concerning our intellectual property or other proprietary rights;

∎ the scalability and commercial viability of our manufacturing methods and processes;

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∎ our expectations regarding government and third-party payor coverage and reimbursement;

∎ our ability to compete in the markets for our product candidates;

∎ the impact of government laws and regulations;

∎ developments relating to our competitors and our industry;

∎ the factors that may impact our financial results;

∎ the successful completion of this offering; and

∎ our expected use of proceeds from this offering.

You should refer to the “Risk Factors” section contained in this prospectus supplement, the accompanying prospectus, the documents incorporated by reference herein and therein and any free writing prospectus that we have authorized for use in connection with this offering for a discussion of important factors that may cause our actual results to differ materially from those expressed or implied by our forward-looking statements. It is not possible for our management to predict all risks, nor can we assess the impact of all factors on our business or the extent to which any factor, or combination of factors, may cause actual results to differ materially from those contained in any forward-looking statements we may make. Given these risks, uncertainties and other factors, many of which are beyond our control, we cannot assure you that the forward-looking statements in this prospectus supplement, the accompanying prospectus, the documents incorporated by reference herein and therein or any free writing prospectus that we have authorized for use in connection with this offering will prove to be accurate, and you should not place undue reliance on these forward-looking statements. Furthermore, if our forward-looking statements prove to be inaccurate, the inaccuracy may be material. In light of the significant uncertainties in these forward-looking statements, you should not regard these statements as a representation or warranty by us or any other person that we will achieve our objectives and plans in any specified timeframe, or at all.

Except as required by law, we assume no obligation to update these forward-looking statements publicly, or to revise any forward-looking statements to reflect events or developments occurring after the date of this prospectus supplement, even if new information becomes available in the future.

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USE OF PROCEEDS

We expect to receive approximately $46.1 million in net proceeds from the sale of 16,115,385 shares of common stock andPre-Funded Warrants to purchase 2,884,615 shares of common stock offered by us in this offering (or approximately $53.1 million if the underwriters exercise their option to purchase additional shares in full), after deducting underwriting discounts and commissions and estimated offering expenses payable by us.

We intend to use the net proceeds from this offering primarily to fund the research and development of our product candidates, acquire or license products or technologies that are complementary to our own, although we have no current plans, commitments or agreements with respect to any acquisitions or licenses as of the date of this prospectus supplement, and for working capital and general corporate purposes.

The expected use of the net proceeds from this offering represents our intentions based upon our current plans and business conditions, which could change in the future as our plans and business conditions evolve. The amounts and timing of our actual expenditures depend on numerous factors, including the progress of our preclinical development efforts, the ongoing status of and results from our clinical trials and other studies and any unforeseen cash needs. As a result, our management will have broad discretion in applying the net proceeds from this offering. Pending the use of the net proceeds from this offering, we intend to invest the net proceeds in short-term, interest-bearing obligations, investment-grade instruments, certificates of deposit or direct or guaranteed obligations of the United States government.

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DILUTION

Investors purchasing our securities in this offering will not experience immediate or substantial dilution in the net tangible book value of their shares of common stock. Our net tangible book value as of September 30, 2019 was $86.5 million, or $4.52 per share. Net tangible book value per share is determined by dividing our total tangible assets, less total liabilities, by the number of shares of our common stock outstanding as of September 30, 2019. Dilution with respect to net tangible book value per share represents the difference between the amount per share paid by investors purchasing shares of common stock in this offering and the as adjusted net tangible book value per share of our common stock immediately after this offering.

After giving effect to the sale of 16,115,385 shares of our common stock andPre-Funded Warrants to purchase 2,884,615 shares of our common stock in this offering at a public offering price of $2.60 per share of common stock and $2.599 perPre-Funded Warrant (which equals the public offering price per share, minus the $0.001 exercise price perPre-Funded Warrant) (and excluding shares of common stock issued and any proceeds received upon exercise of thePre-Funded Warrants or any resulting accounting associated with thePre-Funded Warrants), and after deducting underwriting discounts and commissions and estimated offering expenses payable by us, the as adjusted net tangible book value as of September 30, 2019 would have been approximately $132.6 million, or $3.76 per share. This represents an immediate decrease in net tangible book value of $0.76 per share to existing stockholders and results in no immediate dilution in net tangible book value to investors purchasing our securities in this offering. Instead, investors purchasing our securities in this offering will experience immediate accretion in net tangible book value of $1.16 per share. The following table illustrates this calculation on a per share basis to investors purchasing our securities in this offering:

Public offering price per share			$	2.60
Net tangible book value per share as of September 30, 2019	$	4.52
Decrease in net tangible book value per share attributable to investors purchasing our securities in this offering	$	0.76
As adjusted net tangible book value per share as of September 30, 2019, after giving effect to this offering			$	3.76
Accretion per share to investors purchasing our securities in this offering			$	1.16

Assuming all of thePre-Funded Warrants issued pursuant to this offering were immediately exercised, this would result in an as adjusted net tangible book value per share, after giving effect to this offering and such warrant exercise, of $3.48 per share, which represents an immediate decrease in net tangible book value of $1.04 per share to existing stockholders and results in no immediate dilution in net tangible book value to investors purchasing our securities in this offering. Instead, investors purchasing our securities in this offering would experience immediate accretion in net tangible book value of $0.88 per share.

If the underwriters exercise in full their option to purchase up to 2,850,000 additional shares of common stock at the public offering price of $2.60 per share, the as adjusted net tangible book value after this offering would be approximately $139.6 million, or $3.66 per share, representing an immediate decrease in net tangible book value of $0.86 per share to existing stockholders and results in no immediate dilution in net tangible book value to investors purchasing our securities in this offering. Instead, investors purchasing our securities in this offering would experience immediate accretion in net tangible book value of $1.06 per share.

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The above discussion and table are based on 19,141,645 shares of our common stock outstanding as of September 30, 2019, and excludes:

∎ 3,348,044 shares of our common stock issuable upon the exercise of outstanding stock options as of September 30, 2019 at a weighted average exercise price of $7.39 per share;

∎ 1,574,288 shares of our common stock reserved for future issuance under our 2018 Plan as of September 30, 2019, as well as any future increases in the number of shares of common stock reserved for issuance under our 2018 Plan;

∎ 380,920 shares of our common stock reserved for future issuance under our ESPP as of September 30, 2019, as well as any future increases in the number of shares of common stock reserved for issuance under our ESPP; and

∎ 2,884,615 shares of our common stock underlying thePre-Funded Warrants being offered hereby.

To the extent that options outstanding as of September 30, 2019 have been or may be exercised or other shares of common stock are issued, investors purchasing our common stock in this offering may experience dilution. We will require more capital to pursue our preclinical and clinical activities, regulatory approval and the commercialization of our current or future drug candidates. In addition, we may also choose to raise additional capital due to market conditions or strategic considerations, even if we believe we have sufficient funds for our current or future operating plans. To the extent that additional capital is raised through the sale of equity securities or convertible debt securities, the issuance of these securities could result in dilution to our stockholders.

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DESCRIPTION OFPRE-FUNDED WARRANTS

Pre-Funded Warrants

General

The term“pre-funded” refers to the fact that the purchase price of thePre-Funded Warrants in this offering includes almost the entire exercise price that will be paid under thePre-Funded Warrants, except for a nominal remaining exercise price of $0.001. The purpose of thePre-Funded Warrants is to enable investors that may have restrictions on their ability to beneficially own more than 9.99% of our outstanding common stock following the consummation of this offering the opportunity to invest capital into the Company without triggering their ownership restrictions, by receivingPre-Funded Warrants in lieu of shares of our common stock which would result in such ownership of more than 9.99%, and receiving the ability to exercise their option to purchase the shares underlying thePre-Funded Warrants at a nominal price at a later date.

The following is a brief summary of certain terms and conditions of thePre-Funded Warrants being offered by this prospectus supplement. The following description is subject in all respects to the provisions contained in thePre-Funded Warrants.

Form

ThePre-Funded Warrants will be issued as individual warrant agreements to the investors. The form ofPre-Funded Warrant will be filed as an exhibit to our Current Report on Form8-K that we expect to file with the SEC in connection with this offering.

Exercise price

Pre-Funded Warrants will have an exercise price of $0.001 per share. The exercise price is subject to appropriate adjustment in the event of certain stock dividends and distributions, stock splits, stock combinations, reclassifications or similar events affecting our common stock and also upon any distributions of assets, including cash, stock or other property to our stockholders.

Exercisability

ThePre-Funded Warrants are exercisable at any time after their original issuance. ThePre-Funded Warrants will be exercisable, at the option of each holder, in whole or in part by delivering to us a duly executed exercise notice and by payment in full of the exercise price in immediately available funds for the number of shares of common stock purchased upon such exercise. As an alternative to payment in immediately available funds, the holder may elect to exercisethe Pre-Funded Warrant through a cashless exercise, in which the holder would receive upon such exercise the net number of shares of common stock determined according to the formula set forth in thePre-Funded Warrant. No fractional shares of common stock will be issued in connection with the exercise of aPre-Funded Warrant.

Exercise limitations

The Pre-Funded Warrants may not be exercised by the holder to the extent that the holder, together with its affiliates, would beneficially own, after such exercise more than 9.99% of the shares of our common stock then outstanding (including for such purpose the shares of our common stock issuable upon such exercise). However, any holder may increase or decrease such beneficial ownership limitation upon notice to us, provided that such limitation cannot exceed 19.99%, and provided that any increase in the beneficial ownership limitation shall not be effective until 61 days after such notice is delivered).

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Term

The Pre-Funded Warrants expire 20 years from the date of issuance.

Transferability

Subject to applicable laws, thePre-Funded Warrants may be offered for sale, sold, transferred or assigned without our consent.

Exchange listing

There is no established trading market forthe Pre-Funded Warrants and we do not expect a market to develop. In addition, we do not intend to apply for the listing ofthe Pre-Funded Warrants on any national securities exchange or other trading market. Without an active trading market, the liquidity ofthe Pre-Funded Warrants will be limited.

Fundamental transactions

In the event of a fundamental transaction, as described in thePre-Funded Warrants and generally including any reorganization, recapitalization or reclassification of our common stock, the sale, transfer or other disposition of all or substantially all of our properties or assets, our consolidation or merger with or into another person, the acquisition of more than 50% of our outstanding common stock, or any person or group becoming the beneficial owner of 50% of the voting power represented by our outstanding common stock, upon consummation of such a fundamental transaction, the holders of thePre-Funded Warrants will be entitled to receive upon exercise of thePre-Funded Warrants the kind and amount of securities, cash or other property that the holders would have received had they exercisedthe Pre-funded Warrants immediately prior to such fundamental transaction without regard to any limitations on exercise contained in thePre-Funded Warrants.

No rights as a stockholder

Except by virtue of such holder’s ownership of shares of our common stock, the holder ofa Pre-Funded Warrant does not have the rights or privileges of a holder of our common stock, including any voting rights, until the holder exercises thePre-Funded Warrant.

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MATERIAL U.S. FEDERAL INCOME TAX CONSEQUENCES

The following discussion is a summary of the material U.S. federal income tax consequences of the purchase, ownership and disposition of shares of our common stock orPre-Funded Warrants issued pursuant to this offering, but does not purport to be a complete analysis of all potential tax effects. The effects of other U.S. federal tax laws, such as estate and gift tax laws, and any applicable state, local ornon-U.S. tax laws are not discussed. This discussion is based on the U.S. Internal Revenue Code of 1986, as amended, or the Code, Treasury Regulations promulgated thereunder, judicial decisions, and published rulings and administrative pronouncements of the U.S. Internal Revenue Service, or the IRS, in each case in effect as of the date hereof. These authorities may change or be subject to differing interpretations. Any such change or differing interpretation may be applied retroactively in a manner that could adversely affect a holder. We have not sought and will not seek any rulings from the IRS regarding the matters discussed below. There can be no assurance that the IRS or a court will not take a contrary position to that discussed below regarding the tax consequences of the purchase, ownership and disposition of shares of our common stock orPre-Funded Warrants.

This discussion is limited to holders that hold shares of our common stock orPre-Funded Warrants as “capital assets” within the meaning of Section 1221 of the Code (generally, property held for investment). This discussion does not address all U.S. federal income tax consequences relevant to a holder’s particular circumstances. In addition, it does not address consequences relevant to holders subject to special rules, including, without limitation:

∎ holders that own or are deemed to own more than 5% of our capital stock (except as specifically set forth below);

∎ corporations that accumulate earnings to avoid U.S. federal income tax;

∎ U.S. expatriates and former citizens or long-term residents of the United States;

∎ persons subject to the alternative minimum tax or the Medicare contribution tax on net investment income;

∎ persons for whom shares of our common stock orPre-Funded Warrants constitute qualified small business stock” within the meaning of Section 1202 of the Code;

∎ persons holding shares of our common stock orPre-Funded Warrants as part of a hedge, straddle or other risk reduction strategy or as part of a conversion transaction or other integrated investment;

∎ persons deemed to sell shares of our common stock orPre-Funded Warrants under the constructive sale provisions of the Code;

∎ banks, insurance companies, and other financial institutions;

∎ brokers, dealers or traders in securities or currencies;

∎ “controlled foreign corporations,” “passive foreign investment companies” and corporations that accumulate earnings to avoid U.S. federal income tax;

∎ partnerships or other entities or arrangements treated as partnerships for U.S. federal income tax purposes (and investors therein);

∎ tax-exempt organizations or governmental organizations;

∎ tax-qualified retirement plans;

∎ holders who hold or receive shares of our common stock orPre-Funded Warrants pursuant to the exercise of employee stock options or otherwise as compensation

∎ persons subject to special tax accounting rules under Section 451(b) of the Code; and

∎ “qualified foreign pension funds” as defined in Section 897(l)(2) of the Code and entities all of the interests of which are held by qualified foreign pension funds.

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If an entity treated as a partnership for U.S. federal income tax purposes holds shares of our common stock orPre-Funded Warrants, the tax treatment of a partner in the partnership will depend on the status of the partner, the activities of the partnership and certain determinations made at the partner level. Accordingly, partnerships holding shares of our common stock orPre-Funded Warrants and the partners in such partnerships should consult their tax advisors regarding the U.S. federal income tax consequences to them.

THIS DISCUSSION IS NOT TAX ADVICE. INVESTORS SHOULD CONSULT THEIR TAX ADVISORS WITH RESPECT TO THE APPLICATION OF THE U.S. FEDERAL INCOME TAX LAWS TO THEIR PARTICULAR SITUATIONS AS WELL AS ANY TAX CONSEQUENCES OF THE PURCHASE, OWNERSHIP AND DISPOSITION OF SHARES OF OUR COMMON STOCK ORPRE-FUNDED WARRANTS ARISING UNDER THE U.S. FEDERAL ESTATE OR GIFT TAX LAWS OR UNDER THE LAWS OF ANY STATE, LOCAL ORNON-U.S. TAXING JURISDICTION OR UNDER ANY APPLICABLE INCOME TAX TREATY.

Treatment ofPre-Funded Warrants

Although it is not entirely free from doubt, aPre-Funded Warrant should be treated as a share of our common stock for U.S. federal income tax purposes and a holder ofPre-Funded Warrants should generally be taxed in the same manner as a holder of such shares, as described below. Accordingly, no gain or loss should be recognized upon the exercise of aPre-Funded Warrant and, upon exercise, the holding period of aPre-Funded Warrant should carry over to the share received. Similarly, the tax basis of thePre-Funded Warrant should carry over to the share received upon exercise, increased by the exercise price of $0.001 per share. If aPre-Funded Warrant expires without being exercised, the holder should recognize a capital loss in an amount equal to such holder’s tax basis in thePre-Funded Warrant. This loss will be long-term capital loss if, at the time of the expiration, the holder’s holding period in thePre-Funded Warrant is more than one year. The deductibility of capital losses is subject to limitations.

Our characterization is not binding on the IRS, and the IRS may treat ourPre-Funded Warrants as warrants to acquire shares of our common stock. In that case, the amount and character of your gain with respect to an investment in ourPre-Funded Warrants could be materially different than the discussion set forth below. Accordingly, each holder should consult his, her or its own tax advisor regarding the risks associated with the acquisition ofPre-Funded Warrants pursuant to this offering (including potential alternative characterizations). The balance of this discussion generally assumes that aPre-Funded Warrant is treated as a share of our common stock for U.S. federal income tax purposes.

Tax Considerations Applicable to U.S. Holders

Definition of U.S. Holder

In general, a “U.S. holder” means a beneficial owner of our common stock orPre-Funded Warrants (other than a partnership or an entity or arrangement treated as a partnership for U.S. federal income tax purposes) that is, for U.S. federal income tax purposes:

∎ an individual who is a citizen or resident of the United States;

∎ a corporation, or an entity treated as a corporation for U.S. federal income tax purposes, created or organized in the United States or under the laws of the United States or of any state thereof or the District of Columbia;

∎ an estate, the income of which is subject to U.S. federal income tax regardless of its source; or

∎ a trust if (a) a U.S. court can exercise primary supervision over the trust’s administration and one or more U.S. persons have the authority to control all of the trust’s substantial decisions or (b) the trust has a valid election in effect under applicable U.S. Treasury Regulations to be treated as a U.S. person.

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Distributions on Common Stock

As described in the section entitled “Dividend Policy,” we do not anticipate paying any future distributions on our common stock. However, if we do make distributions on our common stock, such distributions will constitute dividends to the extent paid from our current or accumulated earnings and profits, as determined under U.S. federal income tax principles, and will be includible in your income as ordinary income when received. However, with respect to dividends received by individuals, such dividends generally are taxed at applicable long-term capital gains rates, provided certain holding period requirements are satisfied. If a distribution exceeds our current and accumulated earnings and profits, the excess will be treated as atax-free return of the U.S. holder’s investment, up to such U.S. holder’s adjusted tax basis in the shares of common stock. Any remaining excess will be treated as capital gain from the sale or exchange of such shares, and will be subject to the tax treatment described below in “—Sale or Other Taxable Disposition of the Shares andPre-Funded Warrants.”

Sale or Other Taxable Disposition of Common Stock orPre-Funded Warrant

Upon the sale, exchange or other taxable disposition of shares of common stock orPre-Funded Warrants, a U.S. holder will generally recognize capital gain or loss equal to the difference between the amount of cash and the fair market value of any property received upon the sale, exchange or other taxable disposition and such U.S. holder’s adjusted tax basis in the shares orPre-Funded Warrants. This capital gain or loss will be long-term capital gain or loss if the U.S. holder’s holding period in such shares orPre-Funded Warrants is more than one year at the time of the sale, exchange or other taxable disposition. Long-term capital gains recognized by certainnon-corporate U.S. holders, including individuals, generally will be subject to reduced rates of U.S. federal income tax. The deductibility of capital losses is subject to limitations.

Constructive Dividends onPre-Funded Warrants

Under Section 305 of the Code, an adjustment to (or failure to adjust) the number of shares that will be issued on the exercise of thePre-Funded Warrants, or an adjustment to (or failure to adjust) the exercise price of thePre-Funded Warrants, or any right of the holders of Pre-Funded Warrants to receive upon exercise equivalent property to the property distributed to holders of our common stock, each, an Adjustment, may be treated as a constructive distribution to a U.S. holder of thePre-Funded Warrants. An adjustment (or failure to adjust) may be treated as such a constructive distribution if, and to the extent that, such Adjustment (or failure to adjust) has the effect of increasing such U.S. holder’s proportionate interest in our assets or earnings and profits as determined under U.S. federal income tax principles, depending on the circumstances of such Adjustment (for example, if such Adjustment is to compensate for a distribution of cash or other property to our shareholders). U.S. holders should consult their tax advisors as to (i) whether a constructive dividend deemed paid to anon-corporate U.S. holder would be eligible for the preferential rates of U.S. federal income tax applicable in respect of certain dividends received, (ii) whether corporate holders would be entitled to claim the dividends received deduction with respect to any such constructive dividends, and (iii) the general treatment of constructive distributions under their particular circumstances. Because a constructive dividend deemed received by a U.S. holder would not give rise to any cash from which any applicable withholding could be satisfied, if backup withholding is paid on behalf of a U.S. holder (because such U.S. holder failed to establish an exemption from backup withholding), such backup withholding may be set off against payments on thePre-Funded Warrants or common stock, or offset against other assets of such U.S. holder. Generally, a U.S. holder’s adjusted tax basis in aPre-Funded Warrant will be increased to the extent any such constructive distribution is treated as a dividend. U.S. holders should consult their tax advisors on the impact a constructive distribution may have on their holding period in the Pre-Funded Warrants.

We are required under current law to report the amount of any deemed distributions on our website or to the IRS and to holders ofPre-Funded Warrants not exempt from information reporting. The IRS

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has proposed regulations addressing the amount and timing of deemed distributions, obligations of withholding agents and filing and notice obligations of issuers, effective for deemed distributions occurring on or after the regulations are adopted in final form. If adopted as proposed, the regulations would generally provide that (i) the amount of a deemed distribution is the excess of the fair market value of the right to acquire stock immediately after the Adjustment over the fair market value of the right to acquire stock without the Adjustment, (ii) the deemed distribution occurs at the earlier of the date the Adjustment occurs under the terms of thePre-Funded Warrant and the date of the actual distribution of cash or property that results in the deemed distribution and (iii) subject to certain limited exceptions, a withholding agent is required to impose any applicable withholding on deemed distributions and, if there is no associated cash payment, may set off its withholding obligations against payments on thePre-Funded Warrants or common stock or sales proceeds received by or other funds or assets of an investor, and (iv) we will continue to be required to report the amount of any deemed distributions on our website or to the IRS and to all holders of Pre-Funded Warrants (including holders that would otherwise be exempt from reporting). The final regulations will be effective for deemed distributions occurring on or after the date of adoption, but holders ofPre-Funded Warrants and withholding agents may rely on them prior to that date under certain circumstances.

Backup Withholding and Information Reporting

A U.S. holder may be subject to information reporting and backup withholding when such holder receives payments on our common stock orPre-Funded Warrants (including constructive dividends) or receives proceeds from the sale or other taxable disposition of our common stock orPre-Funded Warrants. Certain U.S. holders are exempt from backup withholding, including C corporations and certaintax-exempt organizations. A U.S. holder will be subject to backup withholding if such holder is not otherwise exempt and such holder:

∎ fails to furnish the holder’s taxpayer identification number, which for an individual is ordinarily his or her social security number;

∎ furnishes an incorrect taxpayer identification number;

∎ is notified by the IRS that the holder previously failed to properly report payments of interest or dividends; or

∎ fails to certify under penalties of perjury that the holder has furnished a correct taxpayer identification number and that the IRS has not notified the holder that the holder is subject to backup withholding.

Backup withholding is not an additional tax. Any amounts withheld under the backup withholding rules may be allowed as a refund or a credit against a U.S. holder’s U.S. federal income tax liability, provided the required information is timely furnished to the IRS. U.S. holders should consult their tax advisors regarding their qualification for an exemption from backup withholding and the procedures for obtaining such an exemption.

Tax Considerations Applicable toNon-U.S. Holders

Definition ofNon-U.S. Holder

For purposes of this discussion, a“non-U.S. holder” is a beneficial owner of shares of our common stock or Pre-Funded Warrants that is neither a U.S. holder nor a partnership or an entity or arrangement treated as a partnership for U.S. federal income tax

Distributions and Constructive Distributions

As described in the section titled “Dividend Policy,” we do not anticipate paying any cash dividends on our capital stock in the foreseeable future. However, if we do make distributions of cash or property on our common stock or if any deemed dividends result from certain Adjustments, or failure to make Adjustments, to the conversion rate or exercise price of thePre-Funded Warrants, as described above

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under “Tax Considerations Applicable to U.S. Holders–Constructive Dividends onPre-Funded Warrants” above, such actual or deemed distributions will constitute dividends for U.S. federal income tax purposes to the extent paid from our current or accumulated earnings and profits, as determined under U.S. federal income tax principles. Amounts not treated as dividends for U.S. federal income tax purposes will constitute a return of capital and first be applied against and reduce anon-U.S. holder’s adjusted tax basis in its common stock orPre-Funded Warrants, but not below zero. Any excess will be treated as capital gain and will be treated as described below under “—Sale or Other Taxable Disposition.”

Subject to the discussion below on effectively connected income, backup withholding and FATCA, dividends paid or deemed paid to anon-U.S. holder will be subject to U.S. federal withholding tax at a rate of 30% of the gross amount of the actual or deemed dividends (or such lower rate specified by an applicable income tax treaty, provided theNon-U.S. Holder furnishes a valid IRSForm W-8BEN orW-8BEN-E (or other applicable documentation) certifying qualification for the lower treaty rate). Because a constructive dividend deemed received by anon-U.S. holder would not give rise to any cash from which any applicable withholding tax could be satisfied, if withholding taxes are paid on behalf of anon-U.S. holder, those withholding taxes may be set off against payments of cash on the common stock) orPre-Funded Warrants or sales proceeds received by or other funds or assets of suchnon-U.S. holder.

Anon-U.S. holder that does not timely furnish the required documentation, but that qualifies for a reduced treaty rate, may obtain a refund of any excess amounts withheld by timely filing an appropriate claim for refund with the IRS.Non-U.S. holders should consult their tax advisors regarding their entitlement to benefits under any applicable tax treaties.

If dividends paid or deemed paid to anon-U.S. holder are effectively connected with thenon-U.S. holder’s conduct of a trade or business within the United States (and, if required by an applicable income tax treaty, thenon-U.S. holder maintains a permanent establishment in the United States to which such dividends are attributable), thenon-U.S. holder will be exempt from the U.S. federal withholding tax described above. To claim the exemption, thenon-U.S. holder must furnish to the applicable withholding agent a valid IRSForm W-8ECI, certifying that the dividends are effectively connected with thenon-U.S. holder’s conduct of a trade or business within the United States.

Any such effectively connected dividends will be subject to U.S. federal income tax on a net income basis at the regular rates. Anon-U.S. holder that is a corporation also may be subject to a branch profits tax at a rate of 30% (or such lower rate specified by an applicable income tax treaty) on such effectively connected dividends, as adjusted for certain items.Non-U.S. holders should consult their tax advisors regarding any applicable tax treaties that may provide for different rules.

Sale or Other Taxable Disposition

Subject to the discussions below regarding backup withholding and FATCA, anon-U.S. holder will not be subject to U.S. federal income tax on any gain realized upon the sale or other taxable disposition of our shares of common stock orPre-Funded Warrants unless:

∎ the gain is effectively connected with thenon-U.S. holder’s conduct of a trade or business within the United States (and, if required by an applicable income tax treaty, thenon-U.S. holder maintains a permanent establishment in the United States to which such gain is attributable);

∎ thenon-U.S. holder is a nonresident alien individual present in the United States for 183 days or more during the taxable year of the disposition and certain other requirements are met; or

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∎ shares of our common stock orPre-Funded Warrants constitute a U.S. real property interest, or USRPI, by reason of our status as a U.S. real property holding corporation, or USRPHC, for U.S. federal income tax purposes.

Gain described in the first bullet point above generally will be subject to U.S. federal income tax on a net income basis at the regular rates. Anon-U.S. holder that is a corporation also may be subject to a branch profits tax at a rate of 30% (or such lower rate specified by an applicable income tax treaty) on such effectively connected gain, as adjusted for certain items.

Gain described in the second bullet point above will be subject to U.S. federal income tax at a rate of 30% (or such lower rate specified by an applicable income tax treaty), which may be offset by certain U.S. source capital losses of thenon-U.S. holder (even though the individual is not considered a resident of the United States), provided thenon-U.S. holder has timely filed U.S. federal income tax returns with respect to such losses.

With respect to the third bullet point above, we believe we currently are not, and do not anticipate becoming, a USRPHC. Because the determination of whether we are a USRPHC depends, however, on the fair market value of our USRPIs relative to the fair market value of ournon-U.S. real property interests and our other business assets, there can be no assurance we currently are not a USRPHC or will not become one in the future. Even if we are or were to become a USRPHC, gain arising from the sale or other taxable disposition by anon-U.S. holder will not be subject to U.S. federal income tax if our common stock is (and assuming that ourPre-Funded Warrants are not) “regularly traded,” as defined by applicable Treasury Regulations, on an established securities market, and suchnon-U.S. holder owned, actually and constructively, 5% or less of our common stock throughout the shorter of the five-year period ending on the date of the sale or other taxable disposition or thenon-U.S. holder’s holding period. OurPre-Funded Warrants are not expected to be regularly traded on an established securities market.

Non-U.S. holders should consult their tax advisors regarding any applicable tax treaties that may provide for different rules.

Information Reporting and Backup Withholding

Payments of dividends on our common stock (and constructive dividends deemed paid) on the Pre-Funded Warrants will not be subject to backup withholding, provided thenon-U.S. holder certifies itsnon-U.S. status, such as by furnishing a valid IRSForm W-8BEN,W-8BEN-E orW-8ECI, or otherwise establishes an exemption. However, information returns are required to be filed with the IRS in connection with any dividends paid or deemed paid to thenon-U.S. holder, regardless of whether any tax was actually withheld. In addition, proceeds of the sale or other taxable disposition of our common stock orPre-Funded Warrants within the United States or conducted through certain U.S.-related brokers generally will not be subject to backup withholding or information reporting if the applicable withholding agent receives the certification described above or thenon-U.S. holder otherwise establishes an exemption. Proceeds of a disposition of our common stock orPre-Funded Warrants conducted through anon-U.S. office of anon-U.S. broker that does not have certain enumerated relationships with the United States generally will not be subject to backup withholding or information reporting.

Copies of information returns that are filed with the IRS may also be made available under the provisions of an applicable treaty or agreement to the tax authorities of the country in which thenon-U.S. holder resides or is established.

Backup withholding is not an additional tax. Any amounts withheld under the backup withholding rules may be allowed as a refund or a credit against anon-U.S. holder’s U.S. federal income tax liability, provided the required information is timely furnished to the IRS.

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Additional Withholding Tax on Payments Made to Foreign Accounts

Withholding taxes may be imposed under Sections 1471 to 1474 of the Code (such Sections commonly referred to as the Foreign Account Tax Compliance Act, or FATCA) on certain types of payments made tonon-U.S. financial institutions and certain othernon-U.S. entities. Specifically, a 30% withholding tax may be imposed on actual or deemed dividends on, or (subject to the proposed Treasury Regulations discussed below) gross proceeds from the sale or other disposition of, our common stock orPre-Funded Warrants paid to a “foreign financial institution” or a“non-financial foreign entity” (each as defined in the Code), unless (1) the foreign financial institution undertakes certain diligence and reporting obligations, (2) thenon-financial foreign entity either certifies it does not have any “substantial United States owners” (as defined in the Code) or furnishes identifying information regarding each substantial United States owner, or (3) the foreign financial institution ornon-financial foreign entity otherwise qualifies for an exemption from these rules. If the payee is a foreign financial institution and is subject to the diligence and reporting requirements in (1) above, it must enter into an agreement with the U.S. Department of the Treasury requiring, among other things, that it undertake to identify accounts held by certain “specified United States persons” or “United States owned foreign entities” (each as defined in the Code), annually report certain information about such accounts, and withhold 30% on certain payments tonon-compliant foreign financial institutions and certain other account holders. Foreign financial institutions located in jurisdictions that have an intergovernmental agreement with the United States governing FATCA may be subject to different rules.

Under applicable Treasury Regulations and administrative guidance, withholding under FATCA generally applies to payments of actual or deemed dividends on our common stock orPre-Funded Warrants. While withholding under FATCA also would have applied to payments of gross proceeds from the sale or other disposition on or after January 1, 2019, proposed Treasury Regulations eliminate FATCA withholding on payments of gross proceeds entirely. Taxpayers generally may rely on these proposed Treasury Regulations until final Treasury Regulations are issued.

Prospective investors should consult their tax advisors regarding the potential application of withholding under FATCA to their investment in our common stock orPre-Funded Warrants.

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UNDERWRITING

We and the underwriters for the offering named below have entered into an underwriting agreement with respect to the securities being offered. Subject to the terms and conditions of the underwriting agreement, each underwriter has severally agreed to purchase from us the number of shares of our common stock andPre-Funded Warrants set forth opposite its name below. Cowen and Company, LLC, Wells Fargo Securities, LLC and William Blair & Company, L.L.C. are the representatives of the underwriters.

Underwriter	Number of Shares		Number of Pre-Funded Warrants
Cowen and Company, LLC		6,929,617		1,240,385
Wells Fargo Securities, LLC		4,592,884		822,115
William Blair & Company, L.L.C.		4,592,884		822,115
Total		16,115,385		2,884,615

Entities affiliated with Morningside, our existing stockholder, and certain of our directors and officers have indicated an interest to purchase up to an aggregate of $30.3 million of the securities offered hereby. However, because these indications of interest are not binding agreements or commitments to purchase, such stockholders or their affiliates may elect to purchase fewer securities or not purchase any securities in this offering. In addition, the underwriters may determine to sell more, fewer or no securities in this offering to such stockholders or their affiliates.

The underwriting agreement provides that the obligations of the underwriters are subject to certain conditions precedent and that the underwriters have agreed, severally and not jointly, to purchase all of the securities sold under the underwriting agreement if any of these securities are purchased, other than those shares covered by the option to purchase additional shares described below. If an underwriter defaults, the underwriting agreement provides that the purchase commitments of thenon-defaulting underwriters may be increased or the underwriting agreement may be terminated.

Our common stock is listed for trading on The Nasdaq Global Select Market under the symbol “KZR.” There is no established public market for thePre-Funded Warrants, and we do not intend to list thePre-Funded Warrants on The Nasdaq Global Select Market, any other national securities exchange or any other nationally recognized trading system.

We have agreed to indemnify the underwriters against specified liabilities, including liabilities under the Securities Act, and to contribute to payments the underwriters may be required to make in respect thereof.

The underwriters are offering the securities, subject to prior sale, when, as and if issued to and accepted by them, subject to approval of legal matters by their counsel and other conditions specified in the underwriting agreement. The underwriters reserve the right to withdraw, cancel or modify offers to the public and to reject orders in whole or in part.

Option to Purchase Additional Shares.    We have granted to the underwriters an option to purchase up to 2,850,000 additional shares of common stock at the public offering price, less the underwriting discounts and commissions. This option is exercisable for a period of 30 days. The number of shares subject to the underwriters’ option will equal 15% of the total number of shares of common stock we are offering plus the shares underlying thePre-Funded Warrants. To the extent that the underwriters exercise this option, the underwriters will purchase additional shares from us in approximately the same proportion as shown in the table above.

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Discounts and Commissions.    The following table shows the public offering price, underwriting discount and commissions and proceeds, before expenses to us. These amounts are shown assuming both no exercise and full exercise of the underwriters’ option to purchase additional shares.

					Total
	Per Share		Per Pre-Funded Warrant		Without Option to Purchase Additional Shares		With Option to Purchase Additional Shares
Public offering price	$	2.60	$	2.599	$	49,397,115	$	56,807,115
Underwriting discount	$	0.156	$	0.156	$	2,963,827	$	3,408,427
Proceeds, before expenses, to us	$	2.444	$	2.443	$	46,433,288	$	53,398,688

The underwriters propose to offer the shares of common stock to the public at the public offering price set forth on the cover page of this prospectus, and thePre-Funded Warrants to certain investors at the public offering price per share, minus $0.001. The underwriters may offer the shares of common stock andPre-Funded Warrants to securities dealers at the public offering price less a concession not in excess of $0.078 per share of common stock and $0.078 perPre-Funded Warrant. If all of the shares andPre-Funded Warrants are not sold at the public offering price, the underwriters may change the offering price and other selling terms.

We estimate that the total expenses of the offering, excluding underwriting discounts and commissions, will be approximately $300,000 and are payable by us. We also have agreed to reimburse the underwriters for up to $25,000 for their FINRA counsel fee. In accordance with FINRA Rule 5110, this reimbursed fee is deemed underwriting compensation for this offering.

Discretionary Accounts.    The underwriters do not intend to confirm sales of the securities to any accounts over which they have discretionary authority.

Stabilization.    In connection with this offering, the underwriters may engage in stabilizing transactions, overallotment transactions, syndicate covering transactions, penalty bids and purchases to cover positions created by short sales.

∎ Stabilizing transactions permit bids to purchase shares of common stock so long as the stabilizing bids do not exceed a specified maximum, and are engaged in for the purpose of preventing or retarding a decline in the market price of the common stock while the offering is in progress.

∎ Overallotment transactions involve sales by the underwriters of shares of common stock in excess of the number of shares the underwriters are obligated to purchase. This creates a syndicate short position which may be either a covered short position or a naked short position. In a covered short position, the number of shares over-allotted by the underwriters is not greater than the number of shares that they may purchase in the overallotment option. In a naked short position, the number of shares involved is greater than the number of shares in the overallotment option. The underwriters may close out any short position by exercising their overallotment option and/or purchasing shares in the open market.

∎ Syndicate covering transactions involve purchases of common stock in the open market after the distribution has been completed in order to cover syndicate short positions. In determining the source of shares to close out the short position, the underwriters will consider, among other things, the price of shares available for purchase in the open market as compared with the price at which they may purchase shares through exercise of the overallotment option. If the underwriters sell more shares than could be covered by exercise of the overallotment option and, therefore, have a naked short position, the position can be closed out only by buying shares in the open market. A naked short position is more likely to be created if the

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underwriters are concerned that after pricing there could be downward pressure on the price of the shares in the open market that could adversely affect investors who purchase in the offering.

∎ Penalty bids permit the representatives to reclaim a selling concession from a syndicate member when the common stock originally sold by that syndicate member is purchased in stabilizing or syndicate covering transactions to cover syndicate short positions.

These stabilizing transactions, syndicate covering transactions and penalty bids may have the effect of raising or maintaining the market price of our common stock or preventing or retarding a decline in the market price of our common stock. As a result, the price of our common stock in the open market may be higher than it would otherwise be in the absence of these transactions. Neither we nor the underwriters make any representation or prediction as to the effect that the transactions described above may have on the price of our common stock. These transactions may be effected on the Nasdaq Stock Market, in theover-the-counter market or otherwise and, if commenced, may be discontinued at any time.

Lock-Up Agreements.    Pursuant to certain‘‘lock-up’’ agreements, we and our executive officers, directors and certain of our other stockholders have agreed, subject to certain exceptions, not to sell, offer to sell, contract to sell, pledge, hypothecate, grant any security interest in or otherwise transfer or dispose of, or enter into any swap, hedge or similar agreement or arrangement that transfers, in whole or in part, the economic risk of ownership of, directly or indirectly, or make any demand for, or request or exercise any right with respect to, the registration under the Securities Act of the offer and sale of our common stock or securities convertible into or exchangeable or exercisable for any common stock, or publicly announce any intention to do any of the foregoing, without the prior written consent of the representatives, for a period of 90 days after the date of the pricing of the offering.

Thislock-up provision applies to common stock and to securities convertible into or exchangeable or exercisable for common stock. The exceptions permit parties to the‘‘lock-up’’ agreements, among other things and subject to restrictions, to: (a) make certain gifts, (b) if the party is a corporation, partnership, limited liability company, trust or other business entity, make transfers to any partners, members, stockholders or trust beneficiaries of the party and (c) make transfers pursuant to a change of control (meaning the consummation of any bona fide third party tender offer, merger, consolidation or other similar transaction made to all holders of such party’s securities the result of which is that any “person” (as defined in Section 13(d)(3) of the Exchange Act), or group of persons, becomes the beneficial owner (as defined in Rules13d-3 and13d-5 of the Exchange Act) of more than 50% of the voting capital stock of the Company) not undertaken for the purpose of avoiding the restrictions imposed by the“lock-up” agreement. In addition, thelock-up provision will not restrict broker-dealers from engaging in market making and similar activities conducted in the ordinary course of their business.

The representatives, in their sole discretion, may release our common stock and other securities subject to thelock-up agreements described above in whole or in part at any time. When determining whether or not to release our common stock and other securities fromlock-up agreements, the representatives will consider, among other factors, the holder’s reasons for requesting the release, the number of shares for which the release is being requested and market conditions at the time of the request.

Canada.    The common stock andPre-Funded Warrants may be sold only to purchasers purchasing, or deemed to be purchasing, as principal that are accredited investors, as defined in National Instrument45-106Prospectus Exemptions or subsection 73.3(1) of theSecurities Act(Ontario), and are permitted clients, as defined in National Instrument31-103Registration Requirements, Exemptions and Ongoing Registrant Obligations. Any resale of the common stock must

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be made in accordance with an exemption from, or in a transaction not subject to, the prospectus requirements of applicable securities laws.

Securities legislation in certain provinces or territories of Canada may provide a purchaser with remedies for rescission or damages if this prospectus supplement (including any amendment thereto) contains a misrepresentation, provided that the remedies for rescission or damages are exercised by the purchaser within the time limit prescribed by the securities legislation of the purchaser’s province or territory. The purchaser should refer to any applicable provisions of the securities legislation of the purchaser’s province or territory for particulars of these rights or consult with a legal advisor.

Pursuant to section 3A.3 of National Instrument33-105Underwriting Conflicts(NI33-105), the underwriters are not required to comply with the disclosure requirements of NI33-105 regarding underwriter conflicts of interest in connection with this offering.

United Kingdom.    In addition, in the United Kingdom, this document is being distributed only to, and is directed only at, and any offer subsequently made may only be directed at persons who are “qualified investors” (as defined in the Prospectus Regulation) (i) who have professional experience in matters relating to investments falling within Article 19(5) of the Financial Services and Markets Act 2000 (Financial Promotion) Order 2005, as amended, or the Order, and/or (ii) who are high net worth companies (or persons to whom it may otherwise be lawfully communicated) falling within Article 49(2)(a) to (d) of the Order and/or (iii) to whom it may otherwise be lawfully communicated (all such persons together being referred to as “relevant persons”) in circumstances which have not resulted and will not result in an offer to the public of the shares in the United Kingdom within the meaning of the Financial Services and Markets Act 2000.

Any person in the United Kingdom that is not a relevant person should not act or rely on the information included in this document or use it as basis for taking any action. In the United Kingdom, any investment or investment activity that this document relates to may be made or taken exclusively by relevant persons.

Switzerland.    The securities will not be offered, directly or indirectly, to the public in Switzerland and this prospectus does not constitute a public offering prospectus as that term is understood pursuant to article 652a or 1156 of the Swiss Federal Code of Obligations.

European Economic Area.    In relation to each Member State of the European Economic Area, each, a Member State, no shares of common stock orPre-Funded Warrants have been offered or will be offered pursuant to the offering to the public in that Member State prior to the publication of a prospectus in relation to the shares of common stock orPre-Funded Warrants which has been approved by the competent authority in that Member State or, where appropriate, approved in another Member State and notified to the competent authority in that Member State, all in accordance with the Prospectus Regulation, except that offers of shares of common stock orPre-Funded Warrants may be made to the public in that Member State at any time under the following exemptions under the Prospectus Regulation:

A. to any legal entity which is a qualified investor as defined under the Prospectus Regulation;

B. to fewer than 150 natural or legal persons (other than qualified investors as defined under the Prospectus Regulation), subject to obtaining the prior consent of the underwriters; or

C. in any other circumstances falling within Article 1(4) of the Prospectus Regulation,

provided that no such offer of shares of common stock orPre-Funded Warrants shall require the Company or any underwriter to publish a prospectus pursuant to Article 3 of the Prospectus Regulation

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or supplement a prospectus pursuant to Article 23 of the Prospectus Regulation and each person who initially acquires any shares of common stock orPre-Funded Warrants or to whom any offer is made will be deemed to have represented, acknowledged and agreed to and with each of the underwriters and the Company that it is a “qualified investor” within the meaning of Article 2(e) of the Prospectus Regulation.

In the case of any shares of common stock orPre-Funded Warrants being offered to a financial intermediary as that term is used in Prospectus Regulation, each such financial intermediary will be deemed to have represented, acknowledged and agreed that the shares of common stock orPre-Funded Warrants acquired by it in the offer have not been acquired ona non-discretionary basis on behalf of, nor have they been acquired with a view to their offer or resale to, persons in circumstances which may give rise to an offer to the public other than their offer or resale in a Member State to qualified investors as so defined or in circumstances in which the prior consent of the underwriters have been obtained to each such proposed offer or resale.

For the purposes of this provision, the expression an “offer to the public” in relation to shares of common stock orPre-Funded Warrants in any Member State means the communication in any form and by any means of sufficient information on the terms of the offer and any shares of common stock orPre-Funded Warrants to be offered so as to enable an investor to decide to purchase or subscribe for any shares of common stock orPre-Funded Warrants, and the expression “Prospectus Regulation” means Regulation (EU) 2017/1129.

We have not authorized and do not authorize the making of any offer of securities through any financial intermediary on our behalf, other than offers made by the underwriters and their respective affiliates, with a view to the final placement of the securities as contemplated in this document. Accordingly, no purchaser of the shares of common stock orPre-Funded Warrants, other than the underwriters, is authorized to make any further offer of shares of common stock orPre-Funded Warrants on our behalf or on behalf of the underwriters.

Electronic Offer, Sale and Distribution of Shares.    A prospectus in electronic format may be made available on the websites maintained by one or more of the underwriters or selling group members, if any, participating in this offering and one or more of the underwriters participating in this offering may distribute prospectuses electronically. The representatives may agree to allocate a number of shares of common stock orPre-Funded Warrants to underwriters and selling group members for sale to their online brokerage account holders. Internet distributions will be allocated by the underwriters and selling group members that will make internet distributions on the same basis as other allocations. Other than the prospectus in electronic format, the information on these websites is not part of this prospectus or the registration statement of which this prospectus forms a part, has not been approved or endorsed by us or any underwriter in its capacity as underwriter, and should not be relied upon by investors.

Other Relationships.    Certain of the underwriters and their affiliates have provided, and may in the future provide, various investment banking, commercial banking and other financial services for us and our affiliates for which they have received, and may in the future receive, customary fees. The underwriters and certain of their affiliates may also communicate independent investment recommendations, market color or trading ideas and/or publish or express independent research views in respect of the common stock and may at any time hold, or recommend to clients that they acquire, long and/or short positions in the common stock.

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LEGAL MATTERS

Cooley LLP, Palo Alto, California, will pass upon the validity of the issuance of the securities being sold in this offering. Certain legal matters related to this offering will be passed upon for the underwriters by Latham & Watkins, LLP, Costa Mesa, California. As of the date of this prospectus supplement, GC&H Investments, LLC, an entity consisting of current and former partners and associates of Cooley LLP, beneficially holds an aggregate of 9,444 shares of our common stock.

EXPERTS

The consolidated financial statements of Kezar Life Sciences, Inc. as of December 31, 2018 and 2017, and for each of the years in the three-year period ended December 31, 2018, have been incorporated by reference herein in reliance upon the report of KPMG LLP, independent registered public accounting firm, incorporated by reference herein, and upon the authority of said firm as experts in accounting and auditing.

WHERE YOU CAN FIND MORE INFORMATION

This prospectus supplement and the accompanying prospectus are part of the registration statement onForm S-3 we filed with the SEC under the Securities Act and do not contain all of the information set forth or incorporated by reference in the registration statement and the exhibits to the registration statement. For further information with respect to us and the securities we are offering under this prospectus supplement, we refer you to the registration statement and the exhibits and schedules filed as a part of the registration statement. We file annual, quarterly and current reports, proxy statements and other information with the SEC. The SEC maintains a website that contains reports, proxy and information statements and other information regarding issuers that file electronically with the SEC, including Kezar. The address of the SEC website is www.sec.gov.

We maintain a website at www.kezarlifesciences.com. Information contained on, or accessible through, our website is not a part of this prospectus supplement or the accompanying prospectus and will not be deemed to be incorporated by reference herein or therein.

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INCORPORATION OF CERTAIN INFORMATION BY REFERENCE

The SEC allows us to “incorporate by reference” information into this prospectus supplement, which means that we can disclose important information to you by referring you to another document filed separately with the SEC. The information incorporated by reference is considered to be part of this prospectus supplement. Information in this prospectus supplement supersedes information incorporated by reference that we filed with the SEC prior to the date of this prospectus supplement. We incorporate by reference into this prospectus supplement the information or documents listed below that we have filed with the SEC (FileNo. 001-38542):

∎ our Annual Report onForm10-K for the fiscal year ended December 31, 2018, filed with the SEC on March 26, 2019;

∎ ourdefinitive Proxy Statement on Schedule 14A, filed with the SEC on April 30, 2019 (excluding those portions that are not incorporated by reference into our Annual Report on Form10-K for the fiscal year ended December 31, 2018);

∎ our Quarterly Reports on Form10-Q for the quarters ended March 31, 2019, June 30, 2019 and September 30, 2019, filed with the SEC onMay  7, 2019,August 7, 2019 andNovember  7, 2019, respectively;

∎ our Current Reports on Form8-K filed with the SEC onJanuary 8, 2019,March 6, 2019,June 13, 2019,June 25, 2019,November 12, 2019,December 19, 2019,January 13, 2020 andJanuary 30, 2020, in each case to the extent the information in such reports is filed and not furnished; and

∎ the description of our common stock contained in our registration statement onForm8-A filed with the SEC on June 19, 2018, including any amendments or reports filed for the purposes of updating this description.

Notwithstanding the statements in the preceding paragraphs, no document, report or exhibit (or portion of any of the foregoing) or any other information that we have “furnished” to the SEC pursuant to the Exchange Act shall be incorporated by reference into this prospectus supplement.

We also incorporate by reference into this prospectus supplement all documents (other than current reports furnished under Item 2.02 or Item 7.01 of Form8-K and exhibits filed on such form that are related to such items) that are filed by us with the SEC pursuant to Sections 13(a), 13(c), 14 or 15(d) of the Exchange Act after the date of this prospectus supplement but prior to the termination of the offering. These documents include periodic reports, such as Annual Reports on Form10-K, Quarterly Reports on Form10-Q and Current Reports on Form8-K, as well as proxy statements.

We will provide to each person, including any beneficial owner, to whom a prospectus is delivered, without charge upon written or oral request, a copy of any or all of the documents that are incorporated by reference into this prospectus but not delivered with the prospectus, including exhibits that are specifically incorporated by reference into such documents. You should direct any requests for documents to Kezar Life Sciences, Inc., Attn: Marc Belsky, Secretary, 4000 Shoreline Court, Suite 300, South San Francisco, California 94080; telephone: (650)822-5600.

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PROSPECTUS

$150,000,000

Common Stock

Preferred Stock

Debt Securities

Warrants

From time to time, we may offer up to $150,000,000 of any combination of the securities described in this prospectus in one or more offerings. We may also offer securities as may be issuable upon conversion, redemption, repurchase, exchange or exercise of any securities registered hereunder, including any applicable antidilution provisions.

This prospectus provides a general description of the securities we may offer. Each time we offer securities, we will provide specific terms of the securities offered in a supplement to this prospectus. We may also authorize one or more free writing prospectuses to be provided to you in connection with these offerings. The prospectus supplement and any related free writing prospectus may also add, update or change information contained in this prospectus. You should carefully read this prospectus, the applicable prospectus supplement and any related free writing prospectus, as well as any documents incorporated by reference, before you invest in any of the securities being offered.

This prospectus may not be used to consummate a sale of any securities unless accompanied by a prospectus supplement.

Our common stock is listed on The Nasdaq Global Select Market, or Nasdaq, under the symbol “KZR.” On June 28, 2019, the last reported sale price of our common stock was $7.71 per share. The applicable prospectus supplement will contain information, where applicable, as to any other listing on Nasdaq or any securities market or other exchange of the securities, if any, covered by the prospectus supplement.

We will sell these securities directly to investors, through agents designated from time to time or to or through underwriters or dealers, on a continuous or delayed basis. For additional information on the methods of sale, you should refer to the section titled “Plan of Distribution” in this prospectus. If any agents or underwriters are involved in the sale of any securities with respect to which this prospectus is being delivered, the names of such agents or underwriters and any applicable fees, commissions, discounts or over-allotment options will be set forth in a prospectus supplement. The price to the public of such securities and the net proceeds we expect to receive from such sale will also be set forth in a prospectus supplement.

Investing in our securities involves a high degree of risk. You should review carefully the risks and uncertainties described under the heading “Risk Factors” contained in the applicable prospectus supplement and any related free writing prospectus, and under similar headings in the other documents that are incorporated by reference into this prospectus as described on page 10 of this prospectus.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or determined if this prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

The date of this prospectus is July 11, 2019.

TABLE OF CONTENTS

ABOUT THIS PROSPECTUS	ii
SUMMARY	1
RISK FACTORS	10
SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTS	11
USE OF PROCEEDS	13
DESCRIPTION OF CAPITAL STOCK	14
DESCRIPTION OF DEBT SECURITIES	20
DESCRIPTION OF WARRANTS	27
LEGAL OWNERSHIP OF SECURITIES	29
PLAN OF DISTRIBUTION	33
LEGAL MATTERS	35
EXPERTS	35
WHERE YOU CAN FIND MORE INFORMATION	36
INCORPORATION OF CERTAIN INFORMATION BY REFERENCE	36

ABOUT THIS PROSPECTUS

This prospectus is a part of a registration statement on FormS-3 that we filed with the Securities and Exchange Commission, or SEC, utilizing a “shelf” registration process. Under this shelf registration process, we may sell any combination of the securities described in this prospectus in one or more offerings up to a total aggregate offering price of $150,000,000. This prospectus provides you with a general description of the securities we may offer.

Each time we sell securities under this prospectus, we will provide a prospectus supplement that will contain specific information about the terms of that offering. We may also authorize one or more free writing prospectuses to be provided to you that may contain material information relating to these offerings. The prospectus supplement and any related free writing prospectus that we may authorize to be provided to you may also add, update or change information contained in this prospectus or in any documents that we have incorporated by reference into this prospectus. You should read this prospectus, any applicable prospectus supplement and any related free writing prospectus, together with the information incorporated herein by reference as described under the heading “Incorporation of Certain Information by Reference,” before investing in any of the securities offered.

THIS PROSPECTUS MAY NOT BE USED TO CONSUMMATE A SALE OF SECURITIES UNLESS IT IS ACCOMPANIED BY A PROSPECTUS SUPPLEMENT.

Neither we, nor any agent, underwriter or dealer has authorized any person to give any information or to make any representation other than those contained or incorporated by reference in this prospectus, any applicable prospectus supplement or any related free writing prospectus prepared by or on behalf of us or to which we have referred you. This prospectus, any applicable supplement to this prospectus or any related free writing prospectus do not constitute an offer to sell or the solicitation of an offer to buy any securities other than the registered securities to which they relate, nor do this prospectus, any applicable supplement to this prospectus or any related free writing prospectus constitute an offer to sell or the solicitation of an offer to buy securities in any jurisdiction to any person to whom it is unlawful to make such offer or solicitation in such jurisdiction.

You should not assume that the information contained in this prospectus, any applicable prospectus supplement or any related free writing prospectus is accurate on any date subsequent to the date set forth on the front of the document or that any information we have incorporated by reference is correct on any date subsequent to the date of the document incorporated by reference, even though this prospectus, any applicable prospectus supplement or any related free writing prospectus is delivered, or securities are sold, on a later date.

This prospectus and the information incorporated herein by reference contains summaries of certain provisions contained in some of the documents described herein, but reference is made to the actual documents for complete information. All of the summaries are qualified in their entirety by the actual documents. Copies of some of the documents referred to herein have been filed, will be filed or will be incorporated by reference as exhibits to the registration statement of which this prospectus is a part, and you may obtain copies of those documents as described below under the heading “Where You Can Find More Information.”

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SUMMARY

The following summary highlights information contained elsewhere in this prospectus. This summary is not complete and does not contain all of the information that you need to consider in making your investment decision. You should carefully read the entire prospectus, the applicable prospectus supplement and any related free writing prospectus, including the risks of investing in our securities discussed under the heading “Risk Factors” contained in the applicable prospectus supplement and any related free writing prospectus, and under similar headings in the other documents that are incorporated by reference into this prospectus. You should also carefully read the information incorporated by reference into this prospectus, including our consolidated financial statements, and the exhibits to the registration statement of which this prospectus is a part.

Unless the context indicates otherwise, references in this prospectus to “Kezar,” “Kezar Life Sciences,” “the Company,” “we,” “us,” “our” and similar references refer to Kezar Life Sciences, Inc. and its wholly owned subsidiaries.

Company Overview

We are a clinical-stage biotechnology company, discovering and developing novel small molecule therapeutics to treat unmet needs in autoimmunity and cancer. Our lead product candidate,KZR-616, afirst-in-class selective immunoproteasome inhibitor, has completed testing in healthy volunteers, and we are now enrolling the MISSION trial, a Phase 1b/2 clinical trial in systemic lupus erythematosus, also known as lupus or SLE, and lupus nephritis. We believe that the immunoproteasome is a validated target for the treatment of a wide variety of autoimmune diseases given the compelling published activity seen withnon-selective proteasome inhibitors administered to patients with severe autoimmune diseases. Our Phase 1a results in healthy volunteers and our preliminary Phase 1b results in patients with SLE provide evidence thatKZR-616 potentially avoids adverse effects caused by currently marketednon-selective proteasome inhibitors, including side effects which we believe prevent them from being utilized as a chronic treatment in autoimmune disorders. We intend to developKZR-616 to address underserved autoimmune diseases. The Phase 2 portion of the MISSION trial will evaluateKZR-616 for treatment of lupus nephritis, which currently has noFDA-approved drugs. We are also leveragingKZR-616’s broad therapeutic potential to develop the product candidate in four additional autoimmune indications: dermatomyositis, or DM; polymyositis, or PM; autoimmune hemolytic anemia, or AIHA; and immune thrombocytopenia, or ITP.

Additionally, we are advancing our novel research platform targeting the Sec61 translocon and the protein secretion pathway to discover and develop small molecule therapeutics targeting oncology indications. We expect to nominate our first clinical candidate in the protein secretion program in 2019. We believe our discovery-stage platform, focused on the protein secretion pathway, has the potential to yield oral small molecule alternatives to currently marketed biologic therapeutics, to act as cytotoxic anti-cancer agents or to block the secretion of novel targets of interest in immuno-oncology or inflammation.

KZR-616: Selective Immunoproteasome Inhibitor

We believe thatKZR-616 has potential for the treatment of multiple autoimmune disease indications. In the last decade, research directed by our Chief Scientific Officer, along with work performed in multiple academic laboratories, has led to over 15 peer-reviewed publications showing that selective immunoproteasome inhibition results in a broad anti-inflammatory response, reducing autoimmune disease in animal models of lupus, lupus nephritis, rheumatoid arthritis, inflammatory bowel disease, multiple sclerosis, Type 1 diabetes and other indications. This immunomodulatory

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response was broadly seen across many cell types of the immune system, including both T cells and B cells, and was demonstrated in a safe andnon-immunosuppressive manner. This is distinct from other agents currently used to treat autoimmunity, which typically target a single cytokine or immune cell type or are broadly immunosuppressive.

Autoimmunity and Selective Inhibition of the Immunoproteasome

Autoimmune disease is an immune response directed against the body’s own healthy cells and tissues. Approximately 50 million people in the United States suffer from more than 100 diagnosed autoimmune diseases according to the American Autoimmune Related Diseases Association, Inc. In indications large and small, there remain significant unmet medical needs and indications with no approved drugs beyond broadly prescribed corticosteroids and similar immunosuppressive regimens. These result in increased risk of infection and malignancy and a wide variety of side effects. In diseases such as lupus nephritis, these regimens do not induce high rates of clinically meaningful responses.

Found in all cells of the body, proteasomes regulate intracellular protein degradation and are essential for many cellular processes such as cell division, cell differentiation and cytokine production. There are two main forms of the proteasome: the constitutive proteasome and the immunoproteasome. In most tissues of the body, the constitutive proteasome is the predominant form. In cells of the immune system, the immunoproteasome is the predominant form. While both forms of the proteasome mediate protein degradation, the two forms of the proteasome accomplish this utilizing different active sites. These active sites are responsible for cleaving and degrading proteins. Selective inhibition of the immunoproteasome has the potential to reduce inflammation by targeting dysfunctional immune cells involved in autoimmunity, such as T cells and B cells, without causing widespread immunosuppression.

Safety and Efficacy of Approved Proteasome Inhibitors

The three proteasome inhibitors approved for the treatment of multiple myeloma, Velcade^® (bortezomib), Kyprolis^® (carfilzomib) and Ninlaro^® (ixazomib), are potent “dual inhibitors” of both the immunoproteasome and the constitutive proteasome. This dual-targeting profile is necessary to make them effective treatments for multiple myeloma. However, dual proteasome inhibition is associated with hematologic issues such as thrombocytopenia, neutropenia and anemia, as well as constitutional toxicities such as fatigue and myalgia. In addition, Velcade and Ninlaro are associated with risk of peripheral neuropathy, likely due to theoff-target activity of these drugs against proteins found in peripheral neurons.

Velcade has demonstrated clinical activity in several autoimmune diseases, including lupus, lupus nephritis, rheumatoid arthritis, immune thrombocytopenia, autoimmune hemolytic anemia, primary Sjögren’s syndrome and graft-versus-host disease. In preclinical models, proteasome inhibition blocked production of most inflammatory cytokines, including many of those targeted by current biologic drugs. However, long-term, chronic administration of Velcade in the setting of autoimmune diseases is not considered feasible due to its side effect profile, in particular hematologic toxicities and risk of peripheral neuropathy. As a result, this promising drug target has remained untapped for use in the chronic treatment of autoimmune diseases.

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We believe we are the only company with a selective immunoproteasome inhibitor that has been nominated as a clinical candidate or is in clinical trials. In addition, we believe thatKZR-616, if successfully developed and approved, may have the ability to become the standard of care across a broad range of autoimmune diseases based on the following expected key attributes:

∎ broad immunomodulatory activity that may allow it to outperform approved therapies and to work in indications where other drugs have failed;

∎ lack of immunosuppression, a key drawback to other approved therapies in autoimmunity; and

∎ avoidance of systemic toxicities associated with dual proteasome inhibitors and the peripheral neuropathy associated with Velcade and Ninlaro.

Phase 1b MISSION Trial ofKZR-616

In March 2018, we began enrolling the Phase 1b portion of the MISSION trial, an open-label dose escalation in patients with active lupus who have received at least one standard therapeutic regimen. The Phase 2 portion is a randomized placebo-controlled, double-blind trial to evaluate the safety and efficacy ofKZR-616 in patients with active proliferative lupus nephritis. The primary endpoints of both portions of the trial are safety and tolerability. Secondary and exploratory endpoints include pharmacokinetics, or PK, pharmacodynamics, or PD, biomarker assessments and measures of efficacy. We are also initiating two additional Phase 2 clinical trials ofKZR-616: the PRESIDIO trial in patients with DM or PM, and the MARINA trial in patients with AIHA or ITP. We estimate the addressable patient population in the United States for lupus, lupus nephritis, DM/PM and AIHA/ITP to be 460,000,100,000-200,000, 70,000 and 140,000, respectively.

In June 2019, at the European League Against Rheumatism (EULAR) annual meeting, we presented initial data from the Phase 1b portion of the MISSION trial showing that repeat dosing ofKZR-616 demonstrated safety and tolerability, as well as broad and consistent improvement across multiple measures of disease activity. As of the data cutoff on May 6, 2019, the Phase 1b portion enrolled 24 SLE patients with a median SLEDAI score of 10 across three cohorts. Weekly subcutaneous administration ofKZR-616 at both 45 mg and at 60 mg (followingstep-up dosing) appeared to be well tolerated and demonstrated rapid and broad immunomodulatory activity as consistently evidenced by positive efficacy data across multiple measures of disease activity, including patient reported outcomes, in those patients (n=11) who completed 13 weeks of treatment. Consistent PD was seen between 45 mg and 60 mgstep-up with target levels of immunoproteasome inhibition achieved. Patients receivingKZR-616 did not experience the hematologic or constitutional toxicities associated with approvednon-specific proteasome inhibitors. Two serious adverse events were reported: one patient had thrombotic microangiopathy, which resulted in the termination of dosing, and one patient had localized herpes zoster, which resolved, and the patient completed theKZR-616 treatment period. The favorable safety profile ofKZR-616 supports the dose levels that will be used in the Phase 2 portion of the MISSION trial evaluating patients with lupus nephritis, as well as the Phase 2 PRESIDIO and MARINA trials.

Phase 1a Clinical Trials ofKZR-616 in Healthy Volunteers

In 2017, we completed a Phase 1a clinical trial to assess the safety, tolerability, PK, PD and immunomodulatory activity ofKZR-616 in 82 healthy volunteers. In this trial,KZR-616 or placebo was administered as a single or repeat weekly subcutaneous administration over four weeks.KZR-616 was generally well tolerated and we observed favorable PK and PD. This trial also identified multiple dose levels that resulted in selective and potent inhibition of the immunoproteasome and demonstrated biologic activity in ex vivo assays. Administration ofKZR-616 to healthy volunteers resulted in a dose-dependent increase in exposure and inhibition of immunoproteasome activity. Selective inhibition of the immunoproteasome over the constitutive proteasome was demonstrated using multiple PD assays, and cytokine levels in ex vivo stimulation assays demonstrated an anti-cytokine effect ofKZR-616

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treatment consistent with preclinical models. Single and repeat weekly administration at doses that resulted in potent inhibition of the immunoproteasome were generally well tolerated. Two of 82 subjects experienced Grade 2 adverse events that were considered adverse drug reactions and were recorded as serious adverse events. These reactions included hypotension, sinus tachycardia, nausea, vomiting, rigors and chills. However, we observed none of the hematologic adverse events that are often seen with Velcade and Kyprolis. In addition, liver or kidney function remained within normal limits, and there were no electrocardiogram abnormalities or prolonged constitutional adverse events with weekly administration ofKZR-616.

In 2019, we completed enrollment of a second study in healthy volunteers (all female) to assess the safety, tolerability, PK and target inhibition of a simplified lyophilized formulation ofKZR-616. This formulation has the potential to improve the ease of drug administration, transportation and storage. In this study, separate cohorts received doses of 60 mg or 75 mg (withstep-up dosing from 30 mg) subcutaneously without occurrence of a serious adverse event.

Protein Secretion and the Sec61 Translocon

We are conducting research and discovery efforts targeting protein secretion pathways as potential therapies for oncology and immuno-oncology indications. In mammalian cells, the secretion of proteins such as cytokines and the expression of cell surface transmembrane proteins such as cytokine receptors involve a process called cotranslational translocation. For most proteins, this process occurs via the Sec61 translocon, a highly conserved multi-subunit protein complex found in the membrane of the endoplasmic reticulum of all cells. Inhibition of the Sec61 translocon with small molecules blocks the secretion of some or all proteins, which can result in several physiologic outcomes, including altered cellular function, inhibition of cytokine release and/or cell death. We believe this platform has the potential to yield oral small molecule alternatives to currently marketed biologic therapeutics to act as cytotoxic anti-cancer agents or to block the secretion of novel targets of interest in inflammation or immuno-oncology.

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Our Pipeline

The following table sets forth the status and initial focus of our lead product candidate and protein secretion program:

Corporate Information

We were incorporated under the laws of the State of Delaware on February 19, 2015. Our principal executive offices are located at 4000 Shoreline Court, Suite 300, South San Francisco, California 94080, and our telephone number is (650)822-5600. In January 2016, we incorporated our wholly owned Australian subsidiary, Kezar Life Sciences Australia Pty Ltd, which is a proprietary company limited by shares. Our corporate website address iswww.kezarlifesciences.com. Information contained on, or accessible through, our website is not a part of this prospectus. We have included our website in this prospectus solely as an inactive textual reference.

“Kezar,” the Kezar logo and other trademarks, trade names or service marks of Kezar Life Sciences, Inc. appearing in this prospectus are the property of Kezar Life Sciences, Inc. All other trademarks, trade names and service marks appearing in this prospectus are the property of their respective owners. Solely for convenience, the trademarks and trade names in this prospectus may be referred to without the^® and^™ symbols, but such references should not be construed as any indicator that their respective owners will not assert their rights thereto.

Implications of Being an Emerging Growth Company and a Smaller Reporting Company

We are an “emerging growth company” as defined in the Jumpstart Our Business Startups Act of 2012, or the JOBS Act. For so long as we remain an emerging growth company, we are permitted and intend to take advantage of specified reduced reporting and other burdens that are otherwise applicable generally to public companies, including:

∎ being permitted to provide only two years of audited financial statements, in addition to any required unaudited interim financial statements, with correspondingly reduced “Management’s Discussion and Analysis of Financial Condition and Results of Operations” disclosure;

∎ not being required to comply with the auditor attestation requirements in the assessment of our internal control over financial reporting;

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∎ not being required to comply with any requirement that may be adopted by the Public Company Accounting Oversight Board regarding mandatory audit firm rotation or a supplement to the auditor’s report providing additional information about the audit and the financial statements;

∎ reduced disclosure obligations regarding executive compensation in our periodic reports, proxy statements and registration statements; and

∎ not being required to hold a nonbinding advisory vote on executive compensation and stockholder approval of any golden parachute payments not previously approved.

We may take advantage of these reporting exemptions until we are no longer an emerging growth company. We will remain an emerging growth company until the earlier of: (i) December 31, 2023; (ii) the last day of the fiscal year in which we have total annual gross revenue of at least $1.07 billion; (iii) the last day of the fiscal year in which we are deemed to be a large accelerated filer, which means the market value of our common stock held bynon-affiliates exceeds $700 million as of June 30 ofsuch fiscal year; or (iv) the date on which we have issued more than $1 billion innon-convertible debt during the prior three-year period. We may choose to take advantage of some or all of these available exemptions. We have taken advantage of some reduced reporting requirements in our public filings. Accordingly, the information that we provide stockholders may be different than the information you receive from other public companies in which you hold stock.

In addition, the JOBS Act provides that an emerging growth company can take advantage of an extended transition period for complying with new or revised accounting standards. This provision allows an emerging growth company to delay the adoption of some accounting standards until those standards would otherwise apply to private companies. We have irrevocably elected not to avail ourselves of delayed adoption of new or revised accounting standards and, therefore, we will be subject to the same requirements to adopt new or revised accounting standards as other public companies that are not emerging growth companies.

We are also a smaller reporting company as defined in the Securities Exchange Act of 1934, as amended, or the Exchange Act. We may continue to be a smaller reporting company even after we are no longer an emerging growth company. We may take advantage of certain of the scaled disclosures available to smaller reporting companies and will be able to take advantage of these scaled disclosures for so long as (i) our voting andnon-voting common stock held by nonaffiliates is less than $250.0 million measured on the last business day of our second fiscal quarter or (ii) our annual revenue is less than $100.0 million during the most recently completed fiscal year and our voting andnon-voting common stock held bynon-affiliates is less than $700.0 million measured on the last business day of our second fiscal quarter.

The Securities We May Offer

We may offer shares of our common stock and preferred stock, various series of debt securities and warrants to purchase any of such securities, up to a total aggregate offering price of $150,000,000 from time to time in one or more offerings under this prospectus, together with any applicable prospectus supplement and any related free writing prospectus, at prices and on terms to be determined by market conditions at the time of the relevant offering. This prospectus provides you with a general description of the securities we may offer. Each time we offer a type or series of securities under this prospectus, we will provide a prospectus supplement that will describe the specific amounts, prices and other important terms of the securities, including, to the extent applicable:

∎ designation or classification;

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∎ aggregate principal amount or aggregate offering price;

∎ maturity;

∎ original issue discount;

∎ rates and times of payment of interest or dividends;

∎ redemption, conversion, exchange or sinking fund terms;

∎ ranking;

∎ restrictive covenants;

∎ voting or other rights;

∎ conversion or exchange prices or rates and any provisions for changes to or adjustments in the conversion or exchange prices or rates and in the securities or other property receivable upon conversion or exchange; and

∎ important U.S. federal income tax considerations.

The prospectus supplement and any related free writing prospectus that we may authorize to be provided to you may also add, update or change information contained in this prospectus or in documents we have incorporated by reference. However, no prospectus supplement or free writing prospectus will offer a security that is not registered and described in this prospectus at the time of the effectiveness of the registration statement of which this prospectus is a part.

We may sell the securities directly to investors or through underwriters, dealers or agents. We, and our underwriters or agents, reserve the right to accept or reject all or part of any proposed purchase of securities. If we do offer securities through underwriters or agents, we will include in the applicable prospectus supplement:

∎ the names of those underwriters or agents;

∎ applicable fees, discounts and commissions to be paid to them;

∎ details regarding over-allotment options, if any; and

∎ the estimated net proceeds to us.

This prospectus may not be used to consummate a sale of securities unless it is accompanied by a prospectus supplement.

Common Stock.    We may issue shares of our common stock from time to time. Each holder of common stock is entitled to one vote for each share on all matters submitted to a vote of the stockholders and does not have cumulative voting rights. Subject to preferences that may apply to any outstanding preferred stock, holders of our common stock are entitled to receive ratably any dividends that our board of directors may declare out of funds legally available for that purpose. In the event of our liquidation, dissolution or winding up, holders of our common stock are entitled to share ratably in all assets remaining after payment of liabilities and the liquidation preference of any outstanding preferred stock. Holders of our common stock have no preemptive, conversion, subscription or other rights, and there are no redemption or sinking fund provisions applicable to our common stock. The rights, preferences and privileges of the holders of our common stock are subject to and may be adversely affected by the rights of the holders of shares of any series of our preferred stock that we may designate in the future. In this prospectus, we have summarized certain general features of our common stock under the heading “Description of Capital Stock—Common Stock.” We urge you, however, to read the applicable prospectus supplement (and any related free writing prospectus that we may authorize to be provided to you) related to any common stock being offered.

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Preferred Stock.    We may issue shares of our preferred stock from time to time, in one or more series. Under our certificate of incorporation, our board of directors has the authority, without further action by our stockholders (unless such stockholder action is required by applicable law or the rules of any stock exchange or market on which our securities are then traded), to issue up to 10,000,000 shares of preferred stock in one or more series and to fix the number, rights, preferences, privileges and restrictions thereof. These rights, preferences and privileges could include dividend rights, conversion rights, voting rights, terms of redemption, liquidation preferences and sinking fund terms, and the number of shares constituting any series or the designation of such series, any or all of which may be greater than the rights of common stock. Any convertible preferred stock we may issue will be convertible into our common stock or exchangeable for our other securities. Conversion may be mandatory or at the holder’s option and would be at prescribed conversion rates.

If we sell any series of preferred stock under this prospectus, we will fix the designations, voting powers, preferences and rights of such series of preferred stock, as well as the qualifications, limitations or restrictions thereof, in the certificate of designation relating to that series. We will file as an exhibit to the registration statement of which this prospectus is a part, or will incorporate by reference from reports that we file with the SEC, the form of any certificate of designation that describes the terms of the series of preferred stock that we are offering before the issuance of the related series of preferred stock. In this prospectus, we have summarized certain general features of the preferred stock under the heading “Description of Capital Stock—Preferred Stock.” We urge you, however, to read the applicable prospectus supplement (and any free writing prospectus that we may authorize to be provided to you) related to the series of preferred stock being offered, as well as the complete certificate of designation that contains the terms of the applicable series of preferred stock.

Debt Securities.    From time to time, we may issue debt securities in one or more series, as either senior or subordinated debt or as senior or subordinated convertible debt. The senior debt securities will rank equally with any other unsecured and unsubordinated debt. The subordinated debt securities will be subordinate and junior in right of payment, to the extent and in the manner described in the instrument governing the debt, to all of our senior indebtedness. Convertible debt securities will be convertible into or exchangeable for our common stock or other securities. Conversion may be mandatory or at the holder’s option and would be at prescribed conversion rates.

Any debt securities issued under this prospectus will be issued under one or more documents called indentures, which are contracts between us and a national banking association or other eligible party, as trustee. In this prospectus, we have summarized certain general features of the debt securities under the heading “Description of Debt Securities.” We urge you, however, to read the applicable prospectus supplement (and any free writing prospectus that we may authorize to be provided to you) related to the series of debt securities being offered, as well as the complete indenture(s) and any supplemental indentures that contain the terms of the debt securities. We have filed a form of indenture as an exhibit to the registration statement of which this prospectus is a part. We will file as exhibits to the registration statement of which this prospectus is a part, or will be incorporated by reference from reports that we file with the SEC, supplemental indentures and forms of debt securities containing the terms of the debt securities being offered.

Warrants.    We may issue warrants for the purchase of common stock, preferred stock or debt securities, in one or more series, from time to time. We may issue warrants independently or in combination with common stock, preferred stock or debt securities. In this prospectus, we have summarized certain general features of the warrants under the heading “Description of Warrants.” We urge you, however, to read the applicable prospectus supplement (and any free writing prospectus that we may authorize to be provided to you) related to the particular series of warrants being offered, as

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well as the complete warrant agreements and warrant certificates that contain the terms of the warrants. We have filed forms of the warrant agreements and forms of warrant certificates containing the terms of the warrants that we may offer as exhibits to the registration statement of which this prospectus is a part. We will file as exhibits to the registration statement of which this prospectus is a part, or will be incorporated by reference from reports that we file with the SEC, the form of warrant or the warrant agreement and warrant certificate, as applicable, that contain the terms of the particular series of warrants we are offering, and any supplemental agreements, before the issuance of such warrants.

Any warrants issued under this prospectus may be evidenced by warrant certificates. Warrants may be issued under a warrant agreement that we enter into with a warrant agent. We will indicate the name and address of the warrant agent, if applicable, in the prospectus supplement relating to the particular series of warrants being offered.

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RISK FACTORS

Investing in our securities involves a high degree of risk. You should carefully review the risks and uncertainties described under the heading “Risk Factors” contained in the applicable prospectus supplement and any related free writing prospectus, and under similar headings in our Annual Report on Form10-K for the year ended December 31, 2018 and in our most recent Quarterly Report on Form10-Q, as updated by our subsequent filings, which are incorporated by reference into this prospectus, before deciding whether to purchase any of the securities being registered pursuant to the registration statement of which this prospectus is a part. Each of the risk factors could adversely affect our business, results of operations, financial condition and cash flows, as well as adversely affect the value of an investment in our securities, and the occurrence of any of these risks might cause you to lose all or part of your investment. Additional risks not presently known to us or that we currently believe are immaterial may also significantly impair our business operations.

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SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTS

This prospectus, and the documents incorporated in this prospectus by reference, contain forward-looking statements. These statements are based on our management’s current beliefs, expectations and assumptions about future events, conditions and results and on information currently available to us. Discussions containing these forward-looking statements may be found, among other places, in the sections titled “Business,” “Risk Factors” and “Management’s Discussion and Analysis of Financial Condition and Results of Operations” incorporated by reference from our most recent Annual Report on Form10-K and our most recent Quarterly Report onForm 10-Q, as well as any amendments thereto, filed with the SEC.

In some cases, you can identify forward-looking statements by terminology such as “as “aim,” “anticipate,” “assume,” “believe,” “contemplate,” “continue,” “could,” “design,” “due,” “estimate,” “expect,” “goal,” “intend,” “may,” “objective,” “plan,” “predict,” “positioned,” “potential,” “seek,” “should,” “target,” “will,” “would” or the negative or plural of those terms, and similar expressions intended to identify statements about the future, although not all forward-looking statements contain these words. These forward-looking statements involve known and unknown risks, uncertainties and other factors that may cause our actual results, levels of activity, performance or achievements to be materially different from the information expressed or implied by these statements.

Any statements in this prospectus, or incorporated herein by reference, about our expectations, beliefs, plans, objectives, assumptions or future events or performance are not historical facts and are forward-looking statements. Within the meaning of Section 27A of the Securities Act and Section 21E of the Exchange Act these forward-looking statements include statements regarding:

∎ our plans to develop and commercialize our product candidates;

∎ the initiation, timing, progress and expected results of our current and future clinical trials and our research and development programs;

∎ our estimates regarding expenses, future revenue, capital requirements and needs for additional financing;

∎ our ability to successfully acquire orin-license additional product candidates or other technology on reasonable terms;

∎ our ability to maintain and establish collaborations or strategic relationships or obtain additional funding;

∎ the timing and likelihood of obtaining regulatory approval of our current and future product candidates;

∎ our expectations regarding the potential market size and the rate and degree of market acceptance of such product candidates;

∎ our ability to fund our working capital requirements and expectations regarding the sufficiency of our capital resources;

∎ the implementation of our business model and strategic plans for our business and product candidates;

∎ the scope of protection we are able to establish and maintain for intellectual property rights and the duration of our patent rights covering our product candidates;

∎ developments or disputes concerning our intellectual property or other proprietary rights;

∎ the scalability and commercial viability of our manufacturing methods and processes;

∎ our expectations regarding government and third-party payor coverage and reimbursement;

∎ our ability to compete in the markets for our product candidates;

∎ the impact of government laws and regulations;

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∎ developments relating to our competitors and our industry;

∎ the factors that may impact our financial results; and

∎ our expected use of proceeds from any offering under this prospectus.

You should refer to the “Risk Factors” section contained in the applicable prospectus supplement and any related free writing prospectus, and under similar headings in the other documents that are incorporated by reference into this prospectus, for a discussion of important factors that may cause our actual results to differ materially from those expressed or implied by our forward-looking statements. Given these risks, uncertainties and other factors, many of which are beyond our control, we cannot assure you that the forward-looking statements in this prospectus will prove to be accurate, and you should not place undue reliance on these forward-looking statements. Furthermore, if our forward-looking statements prove to be inaccurate, the inaccuracy may be material. In light of the significant uncertainties in these forward-looking statements, you should not regard these statements as a representation or warranty by us or any other person that we will achieve our objectives and plans in any specified time frame, or at all.

Except as required by law, we assume no obligation to update these forward-looking statements publicly, or to revise any forward-looking statements to reflect events or developments occurring after the date of this prospectus, even if new information becomes available in the future.

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USE OF PROCEEDS

We will retain broad discretion over the use of the net proceeds from the sale of the securities offered hereby. Except as described in any applicable prospectus supplement or in any free writing prospectuses that we may authorize to be provided to you in connection with a specific offering, we currently intend to use the net proceeds from the sale of the securities offered hereby, if any, to fund research and development, acquire or invest in businesses, products or technologies that are complementary to our own, although we have no current plans, commitments or agreements with respect to any acquisitions as of the date of this prospectus, and for working capital and general corporate purposes. We will set forth in the applicable prospectus supplement or free writing prospectus our intended use for the net proceeds received from the sale of any securities sold pursuant to the prospectus supplement or free writing prospectus. Pending the use of net proceeds, we intend to invest the net proceeds in a variety of capital preservation instruments, including short-term, interest-bearing obligations, investment-grade instruments, certificates of deposit or direct or guaranteed obligations of the United States government.

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DESCRIPTION OF CAPITAL STOCK

The following description of our capital stock and provisions of our amended and restated certificate of incorporation and amended and restated bylaws are summaries. You should also refer to the amended and restated certificate of incorporation and the amended and restated bylaws, which are filed as exhibits to the registration statement of which this prospectus is part.

General

Under our amended and restated certificate of incorporation we are authorized to issue up to 125,000,000 shares of common stock, par value $0.001 per share, and 10,000,000 shares of preferred stock, par value $0.001 per share, all of which shares of preferred stock are undesignated. Our board of directors may establish the rights and preferences of the preferred stock from time to time. As of March 31, 2019, we had outstanding 19,118,421 shares of common stock.

Common Stock

Voting Rights

Each holder of common stock is entitled to one vote for each share on all matters submitted to a vote of the stockholders. The affirmative vote of holders of at least 66²⁄₃% of the voting power of all of the then-outstanding shares of capital stock, voting as a single class, will be required to amend certain provisions of our amended and restated certificate of incorporation, including provisions relating to amending our amended and restated bylaws, the classified board, the size of our board, removal of directors, director liability, vacancies on our board, special meetings, stockholder notices, actions by written consent and exclusive jurisdiction.

Dividends

Subject to preferences that may apply to any outstanding preferred stock, holders of our common stock are entitled to receive ratably any dividends that our board of directors may declare out of funds legally available for that purpose on anon-cumulative basis.

Liquidation

In the event of our liquidation, dissolution or winding up, holders of our common stock are entitled to share ratably in all assets remaining after payment of liabilities and the liquidation preference of any outstanding preferred stock.

Rights and Preferences

Holders of our common stock have no preemptive, conversion, subscription or other rights, and there are no redemption or sinking fund provisions applicable to our common stock. The rights, preferences and privileges of the holders of our common stock are subject to and may be adversely affected by the rights of the holders of shares of any series of our preferred stock that we may designate in the future.

Preferred Stock

Pursuant to our amended and restated certificate of incorporation, our board of directors has the authority, without further action by our stockholders, to issue up to 10,000,000 shares of preferred stock in one or more series and to fix the number, rights, preferences, privileges and restrictions thereof. These rights, preferences and privileges could include dividend rights, conversion rights, voting rights, terms of redemption, liquidation preferences and sinking fund terms, and the number of shares constituting any series or the designation of such series, any or all of which may be greater

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than the rights of common stock. The issuance of our preferred stock could adversely affect the voting power of holders of common stock and the likelihood that such holders will receive dividend payments and payments upon liquidation. In addition, the issuance of preferred stock could have the effect of delaying, deferring or preventing a change of control or other corporate action, or make the removal of management more difficult. Additionally, the issuance of preferred stock may have the effect of decreasing the market price of the common stock.

Our board of directors will fix the designations, voting powers, preferences and rights of each series, as well as the qualifications, limitations or restrictions thereof, of the preferred stock of each series that we offer under this prospectus and applicable prospectus supplements in the certificate of designation relating to that series. We will file as an exhibit to the registration statement of which this prospectus is a part, or will incorporate by reference from reports that we file with the SEC, the form of any certificate of designation that describes the terms of the series of preferred stock we are offering before the issuance of that series of preferred stock. This description will include:

∎ the title and stated value;

∎ the number of shares we are offering;

∎ the liquidation preference per share;

∎ the purchase price per share;

∎ the dividend rate per share, dividend period and payment dates and method of calculation for dividends;

∎ whether dividends will be cumulative ornon-cumulative and, if cumulative, the date from which dividends will accumulate;

∎ our right, if any, to defer payment of dividends and the maximum length of any such deferral period;

∎ the procedures for any auction and remarketing, if any;

∎ the provisions for a sinking fund, if any;

∎ the provisions for redemption or repurchase, if applicable, and any restrictions on our ability to exercise those redemption and repurchase rights;

∎ any listing of the preferred stock on any securities exchange or market;

∎ whether the preferred stock will be convertible into our common stock or other securities of ours, including depositary shares and warrants, and, if applicable, the conversion period, the conversion price, or how it will be calculated, and under what circumstances it may be adjusted;

∎ whether the preferred stock will be exchangeable into debt securities, and, if applicable, the exchange period, the exchange price, or how it will be calculated, and under what circumstances it may be adjusted;

∎ voting rights, if any, of the preferred stock;

∎ preemption rights, if any;

∎ restrictions on transfer, sale or other assignment, if any;

∎ whether interests in the preferred stock will be represented by depositary shares;

∎ a discussion of any material or special U.S. federal income tax considerations applicable to the preferred stock;

∎ the relative ranking and preferences of the preferred stock as to dividend rights and rights if we liquidate, dissolve or wind up our affairs;

∎ any limitations on issuances of any class or series of preferred stock ranking senior to or on a parity with the series of preferred stock being issued as to dividend rights and rights if we liquidate, dissolve or wind up our affairs; and

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∎ any other specific terms, rights, preferences, privileges, qualifications or restrictions of the preferred stock.

The Delaware General Corporation Law, or DGCL, which is the law of the state of our incorporation, provides that the holders of preferred stock will have the right to vote separately as a class (or, in some cases, as a series) on an amendment to our certificate of incorporation if the amendment would change the par value, the powers, preferences or special rights of the class or series so as to adversely affect the class or series, as the case may be, or, unless the certificate of incorporation provided otherwise, the number of authorized shares of the class. This right is in addition to any voting rights that may be provided for in the applicable certificate of designation.

Registration Rights

Certain holders of shares of our common stock have the right to demand that we file a registration statement or request that we cover their shares by a registration statement that we otherwise file, as described below.

Demand Registration Rights

The holders of at least a majority of the shares having demand registration rights may, on not more than one occasion, request that we register all or a portion of their shares of common stock for sale under the Securities Act, subject to certain specified exceptions.

FormS-3 Registration Rights

In addition, holders of at least 30% of the shares having demand registration rights may, on no more than two registrations on FormS-3 within any12-month period, request that we register all or a portion of their common stock for sale under the Securities Act on FormS-3, or any successor form, so long as the aggregate offering price to the public in connection with any such offering is at least $5.0 million, subject to specified conditions and limitations.

Piggyback Registration Rights

If we propose to register any shares of our common stock under the Securities Act either for our own account or for the account of other stockholders, the holders of all shares having “piggyback” registration rights are entitled to notice of the registration and allowed to include all or a portion of their shares of common stock in the registration, subject to specified conditions and limitations.

Other Provisions

In the event that any registration in which the holders of registrable shares participate pursuant to the investors’ rights agreement is an underwritten public offering, the number of registrable shares to be included may, in specified circumstances, be limited due to market conditions.

We will pay all registration expenses, other than underwriting discounts, selling commissions and stock transfer taxes, and the reasonable fees and expenses of a single special counsel for the selling stockholders, related to any demand, piggyback and FormS-3 registration. The investors’ rights agreement contains customary cross-indemnification provisions, pursuant to which we must indemnify the selling stockholders in the event of material misstatements or omissions in the registration statement attributable to us, and they must indemnify us for material misstatements or omissions in the registration statement attributable to them. The demand, piggyback and FormS-3 registration rights described above will expire, with respect to any particular stockholder, no later than five years after our initial public offering, or with respect to any particular holder, at such time that such holder can sell its shares under Rule 144 of the Securities Act during any three-month period.

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Anti-Takeover Provisions

Section 203 of the Delaware General Corporation Law

We are subject to Section 203 of the DGCL, which prohibits a Delaware corporation from engaging in any business combination with any interested stockholder for a period of three years after the date that such stockholder became an interested stockholder, with the following exceptions:

∎ before such date, the board of directors of the corporation approved either the business combination or the transaction that resulted in the stockholder becoming an interested stockholder;

∎ upon completion of the transaction that resulted in the stockholder becoming an interested stockholder, the interested stockholder owned at least 85% of the voting stock of the corporation outstanding at the time the transaction began, excluding for purposes of determining the voting stock outstanding, but not the outstanding voting stock owned by the interested stockholder, those shares owned (i) by persons who are directors and also officers and (ii) employee stock plans in which employee participants do not have the right to determine confidentially whether shares held subject to the plan will be tendered in a tender or exchange offer; or

∎ on or after such date, the business combination is approved by the board of directors and authorized at an annual or special meeting of the stockholders, and not by written consent, by the affirmative vote of at least 66²/₃% of the outstanding voting stock that is not owned by the interested stockholder.

In general, Section 203 defines a “business combination” to include the following:

∎ any merger or consolidation involving the corporation and the interested stockholder;

∎ any sale, transfer, pledge or other disposition of 10% or more of the assets of the corporation involving the interested stockholder;

∎ subject to certain exceptions, any transaction that results in the issuance or transfer by the corporation of any stock of the corporation to the interested stockholder;

∎ any transaction involving the corporation that has the effect of increasing the proportionate share of the stock or any class or series of the corporation beneficially owned by the interested stockholder; or

∎ the receipt by the interested stockholder of the benefit of any loans, advances, guarantees, pledges or other financial benefits by or through the corporation.

In general, Section 203 defines an “interested stockholder” as an entity or person who, together with the entity or person’s affiliates and associates, beneficially owns, or is an affiliate or associate of the corporation and within three years prior to the time of determination of interested stockholder status did own, 15% or more of the outstanding voting stock of the corporation.

Amended and Restated Certificate of Incorporation and Amended and Restated Bylaws

Among other things, our amended and restated certificate of incorporation and amended and restated bylaws will:

∎ permit our board of directors to issue up to 10,000,000 shares of preferred stock, with any rights, preferences and privileges as they may designate, including the right to approve an acquisition or other change in control;

∎ provide that the authorized number of directors may be changed only by resolution of our board of directors;

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∎ provide that our board of directors will be classified into three classes of directors;

∎ provide that, subject to the rights of any series of preferred stock to elect directors, directors may only be removed for cause, which removal may be effected, subject to any limitation imposed by law, by the holders of at least a majority of the voting power of all of our then-outstanding shares of the capital stock entitled to vote generally at an election of directors;

∎ provide that all vacancies, including newly created directorships, may, except as otherwise required by law, be filled by the affirmative vote of a majority of directors then in office, even if less than a quorum;

∎ require that any action to be taken by our stockholders must be effected at a duly called annual or special meeting of stockholders and not be taken by written consent or electronic transmission;

∎ provide that stockholders seeking to present proposals before a meeting of stockholders or to nominate candidates for election as directors at a meeting of stockholders must provide advance notice in writing, and also specify requirements as to the form and content of a stockholder’s notice;

∎ provide that special meetings of our stockholders may be called only by the chairman of our board of directors, our chief executive officer or president or by our board of directors pursuant to a resolution adopted by a majority of the total number of authorized directors; and

∎ not provide for cumulative voting rights, therefore allowing the holders of a majority of the shares of common stock entitled to vote in any election of directors to elect all of the directors standing for election, if they should so choose.

The amendment of any of these provisions would require approval by the holders of at least 66²⁄₃% of the voting power of all of our then-outstanding common stock entitled to vote generally in the election of directors, voting together as a single class.

The combination of these provisions will make it more difficult for our existing stockholders to replace our board of directors as well as for another party to obtain control of us by replacing our board of directors. Because our board of directors has the power to retain and discharge our officers, these provisions could also make it more difficult for existing stockholders or another party to effect a change in management. In addition, the authorization of undesignated preferred stock makes it possible for our board of directors to issue preferred stock with voting or other rights or preferences that could impede the success of any attempt to change our control.

These provisions are intended to enhance the likelihood of continued stability in the composition of our board of directors and its policies and to discourage coercive takeover practices and inadequate takeover bids. These provisions are also designed to reduce our vulnerability to hostile takeovers and to discourage certain tactics that may be used in proxy fights. However, such provisions could have the effect of discouraging others from making tender offers for our shares and may have the effect of delaying changes in our control or management. As a consequence, these provisions may also inhibit fluctuations in the market price of our stock that could result from actual or rumored takeover attempts. We believe that the benefits of these provisions, including increased protection of our potential ability to negotiate with the proponent of an unfriendly or unsolicited proposal to acquire or restructure our company, outweigh the disadvantages of discouraging takeover proposals, because negotiation of takeover proposals could result in an improvement of their terms.

Choice of Forum

Our amended and restated certificate of incorporation will provide that unless we consent in writing to the selection of an alternative forum, the Court of Chancery of the State of Delaware (or, if and only if the Court of Chancery of the State of Delaware lacks subject matter jurisdiction, any state court located within the State of Delaware or, if and only if all such state courts lack subject matter

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jurisdiction, the federal district court for the District of Delaware) will be the exclusive forum for (1) any derivative action or proceeding brought on our behalf, (2) any action or proceeding commenced by any of our stockholders (including any class action) asserting a breach of fiduciary duty owed, or other wrongdoing, by any director, officer, employee or agent to us or our stockholders, (3) any action or proceeding commenced by any of our stockholders (including any class action) asserting a claim against us arising pursuant to the DGCL or our amended and restated certificate of incorporation or our amended and restated bylaws, (4) any action or proceeding commenced by any of our stockholders (including any class action) to interpret, apply, enforce or determine the validity of our amended and restated certificate of incorporation or our amended and restated bylaws, or (5) any action or proceeding commenced by any of our stockholders (including any class action) asserting a claim against us that is governed by the internal affairs doctrine.

Our amended and restated certificate of incorporation further provides that the federal district courts of the United States of America will be the exclusive forum for resolving any complaint asserting a cause of action arising under the Securities Act, referred to as the Federal Forum Provision. However, as disclosed in our Current Report on Form8-K filed with the SEC on June 25, 2019, in light of theSciabacucchi decision issued by the Delaware Court of Chancery in December 2018, finding that provisions similar to the Federal Forum Provision are not valid under Delaware law, we do not currently intend to enforce the Federal Forum provision unless the Sciabacucchi decision is appealed and the Delaware Supreme Court reverses the decision. If the Delaware Supreme Court affirms the Delaware Chancery Court’s decision, we intend to seek approval by our stockholders to amend the amended and restated certificate of incorporation at our next regularly-scheduled annual meeting of stockholders to remove the invalid provision.

Transfer Agent and Registrar

The transfer agent and registrar for our common stock is Computershare Trust Company, N.A. The transfer agent’s address is P.O. Box 505000, Louisville, KY 40233-5000. The transfer agent for any series of preferred stock that we may offer under this prospectus will be named and described in the prospectus supplement for that series.

Listing on The Nasdaq Global Select Market

Our common stock is listed on Nasdaq under the symbol “KZR.”

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DESCRIPTION OF DEBT SECURITIES

We may issue debt securities from time to time, in one or more series, as either senior or subordinated debt or as senior or subordinated convertible debt. While the terms we have summarized below will apply generally to any debt securities that we may offer under this prospectus, we will describe the particular terms of any debt securities that we may offer in more detail in the applicable prospectus supplement. The terms of any debt securities offered under a prospectus supplement may differ from the terms described below. Unless the context requires otherwise, whenever we refer to the indenture, we also are referring to any supplemental indentures that specify the terms of a particular series of debt securities.

We will issue the debt securities under the indenture that we will enter into with the trustee named in the indenture. The indenture will be qualified under the Trust Indenture Act of 1939, as amended, or the Trust Indenture Act. We have filed the form of indenture as an exhibit to the registration statement of which this prospectus is a part, and supplemental indentures and forms of debt securities containing the terms of the debt securities being offered will be filed as exhibits to the registration statement of which this prospectus is a part, or will be incorporated by reference from, reports that we file with the SEC.

The following summary of material provisions of the debt securities and the indenture is subject to, and qualified in its entirety by reference to, all of the provisions of the indenture applicable to a particular series of debt securities. We urge you to read the applicable prospectus supplements and any related free writing prospectuses related to the debt securities that we may offer under this prospectus, as well as the complete indenture that contains the terms of the debt securities.

General

The indenture does not limit the amount of debt securities that we may issue. It provides that we may issue debt securities up to the principal amount that we may authorize and may be in any currency or currency unit that we may designate. Except for the limitations on consolidation, merger and sale of all or substantially all of our assets contained in the indenture, the terms of the indenture do not contain any covenants or other provisions designed to give holders of any debt securities protection against changes in our operations, financial condition or transactions involving us.

We may issue the debt securities issued under the indenture as “discount securities,” which means they may be sold at a discount below their stated principal amount. These debt securities, as well as other debt securities that are not issued at a discount, may be issued with “original issue discount,” or OID, for U.S. federal income tax purposes because of interest payment and other characteristics or terms of the debt securities. Material U.S. federal income tax considerations applicable to debt securities issued with OID will be described in more detail in any applicable prospectus supplement.

We will describe in the applicable prospectus supplement the terms of the series of debt securities being offered, including:

∎ the title of the series of debt securities;

∎ any limit upon the aggregate principal amount that may be issued;

∎ the maturity date or dates;

∎ the form of the debt securities of the series;

∎ the applicability of any guarantees;

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∎ whether or not the debt securities will be secured or unsecured, and the terms of any secured debt;

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∎ whether the debt securities rank as senior debt, senior subordinated debt, subordinated debt or any combination thereof, and the terms of any subordination;

∎ if the price (expressed as a percentage of the aggregate principal amount thereof) at which such debt securities will be issued is a price other than the principal amount thereof, the portion of the principal amount thereof payable upon declaration of acceleration of the maturity thereof, or if applicable, the portion of the principal amount of such debt securities that is convertible into another security or the method by which any such portion shall be determined;

∎ the interest rate or rates, which may be fixed or variable, or the method for determining the rate and the date interest will begin to accrue, the dates interest will be payable and the regular record dates for interest payment dates or the method for determining such dates;

∎ our right, if any, to defer payment of interest and the maximum length of any such deferral period;

∎ if applicable, the date or dates after which, or the period or periods during which, and the price or prices at which, we may, at our option, redeem the series of debt securities pursuant to any optional or provisional redemption provisions and the terms of those redemption provisions;

∎ the date or dates, if any, on which, and the price or prices at which we are obligated, pursuant to any mandatory sinking fund or analogous fund provisions or otherwise, to redeem, or at the holder’s option to purchase, the series of debt securities and the currency or currency unit in which the debt securities are payable;

∎ the denominations in which we will issue the series of debt securities, if other than denominations of $1,000 and any integral multiple thereof;

∎ any and all terms, if applicable, relating to any auction or remarketing of the debt securities of that series and any security for our obligations with respect to such debt securities and any other terms which may be advisable in connection with the marketing of debt securities of that series;

∎ whether the debt securities of the series shall be issued in whole or in part in the form of a global security or securities; the terms and conditions, if any, upon which such global security or securities may be exchanged in whole or in part for other individual securities; and the depositary for such global security or securities;

∎ if applicable, the provisions relating to conversion or exchange of any debt securities of the series and the terms and conditions upon which such debt securities will be so convertible or exchangeable, including the conversion or exchange price, as applicable, or how it will be calculated and may be adjusted, any mandatory or optional (at our option or the holders’ option) conversion or exchange features, the applicable conversion or exchange period and the manner of settlement for any conversion or exchange;

∎ if other than the full principal amount thereof, the portion of the principal amount of debt securities of the series which shall be payable upon declaration of acceleration of the maturity thereof;

∎ additions to or changes in the covenants applicable to the particular debt securities being issued, including, among others, the consolidation, merger or sale covenant;

∎ additions to or changes in the events of default with respect to the securities and any change in the right of the trustee or the holders to declare the principal, premium, if any, and interest, if any, with respect to such securities to be due and payable;

∎ additions to or changes in or deletions of the provisions relating to covenant defeasance and legal defeasance;

∎ additions to or changes in the provisions relating to satisfaction and discharge of the indenture;

∎ additions to or changes in the provisions relating to the modification of the indenture both with and without the consent of holders of debt securities issued under the indenture;

∎ the currency of payment of debt securities if other than U.S. dollars and the manner of determining the equivalent amount in U.S. dollars;

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∎ whether interest will be payable in cash or additional debt securities at our or the holders’ option and the terms and conditions upon which the election may be made;

∎ the terms and conditions, if any, upon which we will pay amounts in addition to the stated interest, premium, if any and principal amounts of the debt securities of the series to any holder that is not a “United States person” for federal tax purposes;

∎ any restrictions on transfer, sale or assignment of the debt securities of the series; and

∎ any other specific terms, preferences, rights or limitations of, or restrictions on, the debt securities, any other additions or changes in the provisions of the indenture, and any terms that may be required by us or advisable under applicable laws or regulations.

Conversion or Exchange Rights

We will set forth in the applicable prospectus supplement the terms on which a series of debt securities may be convertible into or exchangeable for our common stock or our other securities. We will include provisions as to settlement upon conversion or exchange and whether conversion or exchange is mandatory, at the option of the holder or at our option. We may include provisions pursuant to which the number of shares of our common stock or our other securities that the holders of the series of debt securities receive would be subject to adjustment.

Consolidation, Merger or Sale

Unless we provide otherwise in the prospectus supplement applicable to a particular series of debt securities, the indenture will not contain any covenant that restricts our ability to merge or consolidate, or sell, convey, transfer or otherwise dispose of our assets as an entirety or substantially as an entirety. However, any successor to or acquirer of such assets (other than a subsidiary of ours) must assume all of our obligations under the indenture or the debt securities, as appropriate.

Events of Default under the Indenture

Unless we provide otherwise in the prospectus supplement applicable to a particular series of debt securities, the following are events of default under the indenture with respect to any series of debt securities that we may issue:

∎ if we fail to pay any installment of interest on any series of debt securities, as and when the same shall become due and payable, and such default continues for a period of 90 days; provided, however, that a valid extension of an interest payment period by us in accordance with the terms of any indenture supplemental thereto shall not constitute a default in the payment of interest for this purpose;

∎ if we fail to pay the principal of, or premium, if any, on any series of debt securities as and when the same shall become due and payable whether at maturity, upon redemption, by declaration or otherwise, or in any payment required by any sinking or analogous fund established with respect to such series; provided, however, that a valid extension of the maturity of such debt securities in accordance with the terms of any indenture supplemental thereto shall not constitute a default in the payment of principal or premium, if any;

∎ if we fail to observe or perform any other covenant or agreement contained in the debt securities or the indenture, other than a covenant specifically relating to another series of debt securities, and our failure continues for 90 days after we receive written notice of such failure, requiring the same to be remedied and stating that such is a notice of default thereunder, from the trustee or holders of at least 25% in aggregate principal amount of the outstanding debt securities of the applicable series; and

∎ if specified events of bankruptcy, insolvency or reorganization occur.

If an event of default with respect to debt securities of any series occurs and is continuing, other than an event of default specified in the last bullet point above, the trustee or the holders of at least

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25% in aggregate principal amount of the outstanding debt securities of that series, by notice to us in writing, and to the trustee if notice is given by such holders, may declare the unpaid principal of, premium, if any, and accrued interest, if any, due and payable immediately. If an event of default specified in the last bullet point above occurs with respect to us, the principal amount of and accrued interest, if any, of each issue of debt securities then outstanding shall be due and payable without any notice or other action on the part of the trustee or any holder.

The holders of a majority in principal amount of the outstanding debt securities of an affected series may waive any default or event of default with respect to the series and its consequences, except defaults or events of default regarding payment of principal, premium, if any, or interest, unless we have cured the default or event of default in accordance with the indenture. Any waiver shall cure the default or event of default.

Subject to the terms of the indenture, if an event of default under an indenture shall occur and be continuing, the trustee will be under no obligation to exercise any of its rights or powers under such indenture at the request or direction of any of the holders of the applicable series of debt securities, unless such holders have offered the trustee reasonable indemnity. The holders of a majority in principal amount of the outstanding debt securities of any series will have the right to direct the time, method and place of conducting any proceeding for any remedy available to the trustee, or exercising any trust or power conferred on the trustee, with respect to the debt securities of that series, provided that:

∎ the direction so given by the holder is not in conflict with any law or the applicable indenture; and

∎ subject to its duties under the Trust Indenture Act, the trustee need not take any action that might involve it in personal liability or might be unduly prejudicial to the holders not involved in the proceeding.

A holder of the debt securities of any series will have the right to institute a proceeding under the indenture or to appoint a receiver or trustee, or to seek other remedies only if:

∎ the holder has given written notice to the trustee of a continuing event of default with respect to that series;

∎ the holders of at least 25% in aggregate principal amount of the outstanding debt securities of that series have made written request,

∎ such holders have offered to the trustee indemnity satisfactory to it against the costs, expenses and liabilities to be incurred by the trustee in compliance with the request; and

∎ the trustee does not institute the proceeding, and does not receive from the holders of a majority in aggregate principal amount of the outstanding debt securities of that series other conflicting directions within 90 days after the notice, request and offer.

These limitations do not apply to a suit instituted by a holder of debt securities if we default in the payment of the principal, premium, if any, or interest on, the debt securities.

We will periodically file statements with the trustee regarding our compliance with specified covenants in the indenture.

Modification of Indenture; Waiver

We and the trustee may change an indenture without the consent of any holders with respect to specific matters:

∎ to cure any ambiguity, defect or inconsistency in the indenture or in the debt securities of any series;

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∎ to comply with the provisions described above under “Description of Debt Securities—Consolidation, Merger or Sale;”

∎ to provide for uncertificated debt securities in addition to or in place of certificated debt securities;

∎ to add to our covenants, restrictions, conditions or provisions such new covenants, restrictions, conditions or provisions for the benefit of the holders of all or any series of debt securities, to make the occurrence, or the occurrence and the continuance, of a default in any such additional covenants, restrictions, conditions or provisions an event of default or to surrender any right or power conferred upon us in the indenture;

∎ to add to, delete from or revise the conditions, limitations, and restrictions on the authorized amount, terms, or purposes of issue, authentication and delivery of debt securities, as set forth in the indenture;

∎ to make any change that does not adversely affect the interests of any holder of debt securities of any series in any material respect;

∎ to provide for the issuance of and establish the form and terms and conditions of the debt securities of any series as provided above under “Description of Debt Securities—General” to establish the form of any certifications required to be furnished pursuant to the terms of the indenture or any series of debt securities, or to add to the rights of the holders of any series of debt securities;

∎ to evidence and provide for the acceptance of appointment under any indenture by a successor trustee; or

∎ to comply with any requirements of the SEC in connection with the qualification of any indenture under the Trust Indenture Act.

In addition, under the indenture, the rights of holders of a series of debt securities may be changed by us and the trustee with the written consent of the holders of at least a majority in aggregate principal amount of the outstanding debt securities of each series that is affected. However, unless we provide otherwise in the prospectus supplement applicable to a particular series of debt securities, we and the trustee may make the following changes only with the consent of each holder of any outstanding debt securities affected:

∎ extending the fixed maturity of any debt securities of any series;

∎ reducing the principal amount, reducing the rate of or extending the time of payment of interest, or reducing any premium payable upon the redemption of any series of any debt securities; or

∎ reducing the percentage of debt securities, the holders of which are required to consent to any amendment, supplement, modification or waiver.

Discharge

Each indenture provides that we can elect to be discharged from our obligations with respect to one or more series of debt securities, except for specified obligations, including obligations to:

∎ provide for payment;

∎ register the transfer or exchange of debt securities of the series;

∎ replace stolen, lost or mutilated debt securities of the series;

∎ pay principal of and premium and interest on any debt securities of the series;

∎ maintain paying agencies;

∎ hold monies for payment in trust;

∎ recover excess money held by the trustee;

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∎ compensate and indemnify the trustee; and

∎ appoint any successor trustee.

In order to exercise our rights to be discharged, we must deposit with the trustee money or government obligations sufficient to pay all the principal of, any premium, if any, and interest on, the debt securities of the series on the dates payments are due.

Form, Exchange and Transfer

We will issue the debt securities of each series only in fully registered form without coupons and, unless we provide otherwise in the applicable prospectus supplement, in denominations of $1,000 and any integral multiple thereof. The indenture provides that we may issue debt securities of a series in temporary or permanent global form and as book-entry securities that will be deposited with, or on behalf of, The Depository Trust Company, or the DTC, or another depositary named by us and identified in the applicable prospectus supplement with respect to that series. To the extent the debt securities of a series are issued in global form and as book-entry, a description of terms relating to any book-entry securities will be set forth in the applicable prospectus supplement.

At the option of the holder, subject to the terms of the indenture and the limitations applicable to global securities described in the applicable prospectus supplement, the holder of the debt securities of any series can exchange the debt securities for other debt securities of the same series, in any authorized denomination and of like tenor and aggregate principal amount.

Subject to the terms of the indenture and the limitations applicable to global securities set forth in the applicable prospectus supplement, holders of the debt securities may present the debt securities for exchange or for registration of transfer, duly endorsed or with the form of transfer endorsed thereon duly executed if so required by us or the security registrar, at the office of the security registrar or at the office of any transfer agent designated by us for this purpose. Unless otherwise provided in the debt securities that the holder presents for transfer or exchange, we will impose no service charge for any registration of transfer or exchange, but we may require payment of any taxes or other governmental charges.

We will name in the applicable prospectus supplement the security registrar, and any transfer agent in addition to the security registrar, that we initially designate for any debt securities. We may at any time designate additional transfer agents or rescind the designation of any transfer agent or approve a change in the office through which any transfer agent acts, except that we will be required to maintain a transfer agent in each place of payment for the debt securities of each series.

If we elect to redeem the debt securities of any series, we will not be required to:

∎ issue, register the transfer of, or exchange any debt securities of that series during a period beginning at the opening of business 15 days before the day of mailing of a notice of redemption of any debt securities that may be selected for redemption and ending at the close of business on the day of the mailing; or

∎ register the transfer of or exchange any debt securities so selected for redemption, in whole or in part, except the unredeemed portion of any debt securities we are redeeming in part.

Information Concerning the Trustee

The trustee, other than during the occurrence and continuance of an event of default under an indenture, undertakes to perform only those duties as are specifically set forth in the applicable indenture. Upon an event of default under an indenture, the trustee must use the same degree of care as a prudent person would exercise or use in the conduct of his or her own affairs. Subject to this

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provision, the trustee is under no obligation to exercise any of the powers given it by the indenture at the request of any holder of debt securities unless it is offered reasonable security and indemnity against the costs, expenses and liabilities that it might incur.

Payment and Paying Agents

Unless we otherwise indicate in the applicable prospectus supplement, we will make payment of the interest on any debt securities on any interest payment date to the person in whose name the debt securities, or one or more predecessor securities, are registered at the close of business on the regular record date for the interest.

We will pay principal of and any premium and interest on the debt securities of a particular series at the office of the paying agents designated by us, except that unless we otherwise indicate in the applicable prospectus supplement, we will make interest payments by check that we will mail to the holder or by wire transfer to certain holders. Unless we otherwise indicate in the applicable prospectus supplement, we will designate the corporate trust office of the trustee as our sole paying agent for payments with respect to debt securities of each series. We will name in the applicable prospectus supplement any other paying agents that we initially designate for the debt securities of a particular series. We will maintain a paying agent in each place of payment for the debt securities of a particular series.

All money we pay to a paying agent or the trustee for the payment of the principal of or any premium or interest on any debt securities that remains unclaimed at the end of two years after such principal, premium or interest has become due and payable will be repaid to us, and the holder of the debt security thereafter may look only to us for payment thereof.

Governing Law

The indenture and the debt securities will be governed by and construed in accordance with the internal laws of the State of New York, except to the extent that the Trust Indenture Act of 1939 is applicable.

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DESCRIPTION OF WARRANTS

The following description, together with the additional information we may include in any applicable prospectus supplement and in any related free writing prospectus that we may authorize to be distributed to you, summarizes the material terms and provisions of the warrants that we may offer under this prospectus, which may consist of warrants to purchase common stock, preferred stock or debt securities and may be issued in one or more series. Warrants may be offered independently or in combination with common stock, preferred stock or debt securities offered by any prospectus supplement. While the terms we have summarized below will apply generally to any warrants that we may offer under this prospectus, we will describe the particular terms of any series of warrants in more detail in the applicable prospectus supplement. The following description of warrants will apply to the warrants offered by this prospectus unless we provide otherwise in the applicable prospectus supplement. The applicable prospectus supplement for a particular series of warrants may specify different or additional terms.

We have filed forms of the warrant agreements and forms of warrant certificates listing the terms of the warrants that may be offered as exhibits to the registration statement of which this prospectus is a part. We will file as exhibits to the registration statement of which this prospectus is a part, or will incorporate by reference from reports that we file with the SEC, the form of warrant or the warrant agreement and warrant certificate, as applicable, that contain the terms of the particular series of warrants we are offering, as well as any supplemental agreements, before the issuance of such warrants. The following summaries of material terms and provisions of the warrants are subject to, and qualified in their entirety by reference to, all the provisions of the form of warrant or the warrant agreement and warrant certificate, as applicable, and any supplemental agreements applicable to a particular series of warrants that we may offer under this prospectus. We urge you to read the applicable prospectus supplement related to the particular series of warrants that we may offer under this prospectus, as well as any related free writing prospectus, and the complete form of warrant or the warrant agreement and warrant certificate, as applicable, and any supplemental agreements, that list the terms of the warrants.

General

In the applicable prospectus supplement, we will describe the terms of the series of warrants being offered, including, to the extent applicable:

∎ the offering price and aggregate number of warrants offered;

∎ the currency for which the warrants may be purchased;

∎ the designation and terms of the securities with which the warrants are issued and the number of warrants issued with each such security or each principal amount of such security;

∎ in the case of warrants to purchase debt securities, the principal amount of debt securities purchasable on exercise of one warrant and the price at, and currency in which, this principal amount of debt securities may be purchased on such exercise;

∎ in the case of warrants to purchase common stock or preferred stock, the number of shares of common stock or preferred stock, as the case may be, purchasable on the exercise of one warrant and the price at which these shares may be purchased on such exercise;

∎ the effect of any merger, consolidation, sale or other disposition of our business on the warrant agreements and the warrants;

∎ the terms of any rights to redeem or call the warrants;

∎ any provisions for changes to or adjustments in the exercise price or number of securities issuable on exercise of the warrants;

∎ the dates on which the right to exercise the warrants will commence and expire;

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∎ the manner in which the warrant agreements and warrants may be modified;

∎ a discussion of material or special U.S. federal income tax considerations of holding or exercising the warrants;

∎ the terms of the securities issuable on exercise of the warrants; and

∎ any other specific terms, preferences, rights or limitations of or restrictions on the warrants.

Before exercising their warrants, holders of warrants will not have any of the rights of holders of the securities purchasable on such exercise, including:

∎ in the case of warrants to purchase common stock or preferred stock, the right to receive dividends, if any, or payments on our liquidation, dissolution or winding up or to exercise voting rights, if any; or

∎ in the case of warrants to purchase debt securities, the right to receive payments of principal of, or premium, if any, or interest on, the debt securities purchasable on exercise or to enforce covenants in the applicable indenture.

Exercise of Warrants

Each warrant will entitle the holder to purchase the securities that we specify in the applicable prospectus supplement at the exercise price that we describe in the applicable prospectus supplement. The warrants may be exercised as listed in the prospectus supplement relating to the warrants offered. Unless we otherwise specify in the applicable prospectus supplement, warrants may be exercised at any time up to the specified time on the expiration date that we list in the applicable prospectus supplement. After the close of business on the expiration date, unexercised warrants will become void.

On receipt of payment and the warrant or warrant certificate, as applicable, properly completed and duly executed at the corporate trust office of the warrant agent, if any, or any other office, including ours, indicated in the prospectus supplement, we will, as soon as practicable, issue and deliver the securities purchasable on such exercise. If less than all of the warrants (or the warrants represented by such warrant certificate) are exercised, a new warrant or a new warrant certificate, as applicable, will be issued for the remaining warrants.

Governing Law

Unless we provide otherwise in the applicable prospectus supplement, the warrants and warrant agreements will be governed by and construed in accordance with the laws of the State of New York.

Enforceability of Rights by Holders of Warrants

Each warrant agent, if any, will act solely as our agent under the applicable warrant agreement and will not assume any obligation or relationship of agency or trust with any holder of any warrant. A single bank or trust company may act as warrant agent for more than one issue of warrants. A warrant agent will have no duty or responsibility in case of any default by us under the applicable warrant agreement or warrant, including any duty or responsibility to initiate any proceedings at law or otherwise, or to make any demand on us. Any holder of a warrant may, without the consent of the related warrant agent or the holder of any other warrant, enforce by appropriate legal action its right to exercise, and receive the securities purchasable on exercise of, its warrants.

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LEGAL OWNERSHIP OF SECURITIES

We can issue securities in registered form or in the form of one or more global securities. We describe global securities in greater detail below. We refer to those persons who have securities registered in their own names on the books that we or any applicable trustee or depositary maintain for this purpose as the “holders” of those securities. These persons are the legal holders of the securities. We refer to those persons who, indirectly through others, own beneficial interests in securities that are not registered in their own names, as “indirect holders” of those securities. As we discuss below, indirect holders are not legal holders, and investors in securities issued in book-entry form or in street name will be indirect holders.

Book-Entry Holders

We may issue securities in book-entry form only, as we will specify in the applicable prospectus supplement. This means securities may be represented by one or more global securities registered in the name of a financial institution that holds them as depositary on behalf of other financial institutions that participate in the depositary’s book-entry system. These participating institutions, which are referred to as participants, in turn, hold beneficial interests in the securities on behalf of themselves or their customers.

Only the person in whose name a security is registered is recognized as the holder of that security. Global securities will be registered in the name of the depositary or its participants. Consequently, for global securities, we will recognize only the depositary as the holder of the securities, and we will make all payments on the securities to the depositary. The depositary passes along the payments it receives to its participants, which in turn pass the payments along to their customers who are the beneficial owners. The depositary and its participants do so under agreements they have made with one another or with their customers; they are not obligated to do so under the terms of the securities.

As a result, investors in a global security will not own securities directly. Instead, they will own beneficial interests in a global security, through a bank, broker or other financial institution that participates in the depositary’s book-entry system or holds an interest through a participant. As long as the securities are issued in global form, investors will be indirect holders, and not legal holders, of the securities.

Street Name Holders

We may terminate a global security or issue securities that are not issued in global form. In these cases, investors may choose to hold their securities in their own names or in “street name.” Securities held by an investor in street name would be registered in the name of a bank, broker or other financial institution that the investor chooses, and the investor would hold only a beneficial interest in those securities through an account he or she maintains at that institution.

For securities held in street name, we or any applicable trustee or depositary will recognize only the intermediary banks, brokers and other financial institutions in whose names the securities are registered as the holders of those securities, and we or any such trustee or depositary will make all payments on those securities to them. These institutions pass along the payments they receive to their customers who are the beneficial owners, but only because they agree to do so in their customer agreements or because they are legally required to do so. Investors who hold securities in street name will be indirect holders, not holders, of those securities.

Legal Holders

Our obligations, as well as the obligations of any applicable trustee or third party employed by us or a trustee, run only to the legal holders of the securities. We do not have obligations to investors who

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hold beneficial interests in global securities, in street name or by any other indirect means. This will be the case whether an investor chooses to be an indirect holder of a security or has no choice because we are issuing the securities only in global form.

For example, once we make a payment or give a notice to the holder, we have no further responsibility for the payment or notice even if that holder is required, under agreements with its participants or customers or by law, to pass it along to the indirect holders but does not do so. Similarly, we may want to obtain the approval of the holders to amend an indenture, to relieve us of the consequences of a default or of our obligation to comply with a particular provision of an indenture, or for other purposes. In such an event, we would seek approval only from the holders, and not the indirect holders, of the securities. Whether and how the legal holders contact the indirect holders is up to the legal holders.

Special Considerations for Indirect Holders

If you hold securities through a bank, broker or other financial institution, either in book-entry form because the securities are represented by one or more global securities or in street name, you should check with your own institution to find out:

∎ how it handles securities payments and notices;

∎ whether it imposes fees or charges;

∎ how it would handle a request for the holders’ consent, if ever required;

∎ whether and how you can instruct it to send you securities registered in your own name so you can be a holder, if that is permitted in the future;

∎ how it would exercise rights under the securities if there were a default or other event triggering the need for holders to act to protect their interests; and

∎ if the securities are in book-entry form, how the depositary’s rules and procedures will affect these matters.

Global Securities

A global security is a security that represents one or any other number of individual securities held by a depositary. Generally, all securities represented by the same global securities will have the same terms.

Each security issued in book-entry form will be represented by a global security that we issue to, deposit with and register in the name of a financial institution or its nominee that we select. The financial institution that we select for this purpose is called the depositary. Unless we specify otherwise in the applicable prospectus supplement, the DTC, New York, New York, will be the depositary for all securities issued in book-entry form.

A global security may not be transferred to or registered in the name of anyone other than the depositary, its nominee or a successor depositary, unless special termination situations arise. We describe those situations below under “—Special Situations When a Global Security Will Be Terminated.” As a result of these arrangements, the depositary, or its nominee, will be the sole registered owner and legal holder of all securities represented by a global security, and investors will be permitted to own only beneficial interests in a global security. Beneficial interests must be held by means of an account with a broker, bank or other financial institution that in turn has an account with the depositary or with another institution that does. Thus, an investor whose security is represented by a global security will not be a legal holder of the security, but only an indirect holder of a beneficial interest in the global security.

If the prospectus supplement for a particular security indicates that the security will be issued as a global security, then the security will be represented by a global security at all times unless and until

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the global security is terminated. If termination occurs, we may issue the securities through another book-entry clearing system or decide that the securities may no longer be held through any book-entry clearing system.

Special Considerations for Global Securities

As an indirect holder, an investor’s rights relating to a global security will be governed by the account rules of the investor’s financial institution and of the depositary, as well as general laws relating to securities transfers. We do not recognize an indirect holder as a holder of securities and instead deal only with the depositary that holds the global security.

If securities are issued only as global securities, an investor should be aware of the following:

∎ an investor cannot cause the securities to be registered in his or her name, and cannot obtainnon-global certificates for his or her interest in the securities, except in the special situations we describe below;

∎ an investor will be an indirect holder and must look to his or her own bank or broker for payments on the securities and protection of his or her legal rights relating to the securities, as we describe above;

∎ an investor may not be able to sell interests in the securities to some insurance companies and to other institutions that are required by law to own their securities innon-book-entry form;

∎ an investor may not be able to pledge his or her interest in the global security in circumstances where certificates representing the securities must be delivered to the lender or other beneficiary of the pledge in order for the pledge to be effective;

∎ the depositary’s policies, which may change from time to time, will govern payments, transfers, exchanges and other matters relating to an investor’s interest in the global security;

∎ we and any applicable trustee have no responsibility for any aspect of the depositary’s actions or for its records of ownership interests in the global security, nor will we or any applicable trustee supervise the depositary in any way;

∎ the depositary may, and we understand that the DTC will, require that those who purchase and sell interests in the global security within its book-entry system use immediately available funds, and your broker or bank may require you to do so as well; and

∎ financial institutions that participate in the depositary’s book-entry system, and through which an investor holds its interest in the global security, may also have their own policies affecting payments, notices and other matters relating to the securities.

There may be more than one financial intermediary in the chain of ownership for an investor. We do not monitor and are not responsible for the actions of any of those intermediaries.

Special Situations When a Global Security Will Be Terminated

In a few special situations described below, a global security will terminate and interests in it will be exchanged for physical certificates representing those interests. After that exchange, the choice of whether to hold securities directly or in street name will be up to the investor. Investors must consult their own banks or brokers to find out how to have their interests in securities transferred to their own names, so that they will be direct holders. We have described the rights of holders and street name investors above.

Unless we provide otherwise in the applicable prospectus supplement, the global security will terminate when the following special situations occur:

∎ if the depositary notifies us that it is unwilling, unable or no longer qualified to continue as depositary for that global security and we do not appoint another institution to act as depositary within 90 days;

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∎ if we notify any applicable trustee that we wish to terminate that global security; or

∎ if an event of default has occurred with regard to securities represented by that global security and has not been cured or waived.

The applicable prospectus supplement may also list additional situations for terminating a global security that would apply only to the particular series of securities covered by the prospectus supplement. When a global security terminates, the depositary, and neither we nor any applicable trustee, is responsible for deciding the names of the institutions that will be the initial direct holders.

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PLAN OF DISTRIBUTION

We may sell the securities from time to time pursuant to underwritten public offerings, negotiated transactions, block trades or a combination of these methods. We may sell the securities to or through underwriters or dealers, through agents, or directly to one or more purchasers. We may distribute securities from time to time in one or more transactions:

∎ at a fixed price or prices, which may be changed;

∎ at market prices prevailing at the time of sale;

∎ at prices related to such prevailing market prices; or

∎ at negotiated prices.

We may also sell equity securities covered by this registration statement in an “at the market offering” as defined in Rule 415 under the Securities Act. Such offering may be made into an existing trading market for such securities in transactions at other than a fixed price, either:

∎ on or through the facilities of Nasdaq or any other securities exchange or quotation or trading service on which such securities may be listed, quoted or traded at the time of sale; and/or

∎ other than on Nasdaq or such other securities exchanges or quotation or trading services.

Such at the market offerings, if any, may be conducted by underwriters acting as principal or agent.

A prospectus supplement or supplements (and any related free writing prospectus that we may authorize to be provided to you) will describe the terms of the offering of the securities, including, to the extent applicable:

∎ the name or names of any underwriters, dealers or agents, if any;

∎ the purchase price of the securities and the proceeds we will receive from the sale;

∎ any over-allotment options under which underwriters may purchase additional securities from us;

∎ any agency fees or underwriting discounts and other items constituting agents’ or underwriters’ compensation;

∎ any public offering price;

∎ any discounts or concessions allowed or reallowed or paid to dealers; and

∎ any securities exchange or market on which the securities may be listed.

Only underwriters named in the prospectus supplement are underwriters of the securities offered by the prospectus supplement.

If underwriters are used in the sale, they will acquire the securities for their own account and may resell the securities from time to time in one or more transactions at a fixed public offering price or at varying prices determined at the time of sale. The obligations of the underwriters to purchase the securities will be subject to the conditions set forth in the applicable underwriting agreement. We may offer the securities to the public through underwriting syndicates represented by managing underwriters or by underwriters without a syndicate. Subject to certain conditions, the underwriters will be obligated to purchase all of the securities offered by the prospectus supplement. Any public offering price and any discounts or concessions allowed or reallowed or paid to dealers may change from time to time. We may use underwriters with whom we have a material relationship. We will describe in the prospectus supplement, naming the underwriter, the nature of any such relationship.

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We may sell securities directly or through agents we designate from time to time. We will name any agent involved in the offering and sale of securities, and we will describe any commissions we will pay the agent in the prospectus supplement. Unless the prospectus supplement states otherwise, our agent will act on a best-efforts basis for the period of its appointment.

We may authorize agents or underwriters to solicit offers by certain types of institutional investors to purchase securities from us at the public offering price set forth in the prospectus supplement pursuant to delayed delivery contracts providing for payment and delivery on a specified date in the future. We will describe the conditions to these contracts and the commissions we must pay for solicitation of these contracts in the prospectus supplement.

We may provide agents and underwriters with indemnification against civil liabilities related to this offering, including liabilities under the Securities Act, or contribution with respect to payments that the agents or underwriters may make with respect to these liabilities. Agents and underwriters may engage in transactions with, or perform services for, us in the ordinary course of business.

All securities we offer, other than common stock, will be new issues of securities with no established trading market. Any underwriters may make a market in these securities, but will not be obligated to do so and may discontinue any market making at any time without notice. We cannot guarantee the liquidity of the trading markets for any securities.

Any underwriter may engage in overallotment, stabilizing transactions, short covering transactions and penalty bids. Overallotment involves sales in excess of the offering size, which create a short position. Stabilizing transactions permit bids to purchase the underlying security so long as the stabilizing bids do not exceed a specified maximum. Short covering transactions involve purchases of the securities in the open market after the distribution is completed to cover short positions. Penalty bids permit the underwriters to reclaim a selling concession from a dealer when the securities originally sold by the dealer are purchased in a stabilizing or covering transaction to cover short positions. Those activities may cause the price of the securities to be higher than it would otherwise be. If commenced, the underwriters may discontinue any of the activities at any time. These transactions may be effected on any exchange orover-the-counter market or otherwise.

Any underwriters who are qualified market makers on Nasdaq may engage in passive market making transactions in the securities on Nasdaq in accordance with Rule 103 of Regulation M, during the business day prior to the pricing of the offering, before the commencement of offers or sales of the securities. Passive market makers must comply with applicable volume and price limitations and must be identified as passive market makers. In general, a passive market maker must display its bid at a price not in excess of the highest independent bid for such security; if all independent bids are lowered below the passive market maker’s bid, however, the passive market maker’s bid must then be lowered when certain purchase limits are exceeded. Passive market making may stabilize the market price of the securities at a level above that which might otherwise prevail in the open market and, if commenced, may be discontinued at any time.

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LEGAL MATTERS

Unless otherwise indicated in the applicable prospectus supplement, certain legal matters in connection with the offering and the validity of the securities offered by this prospectus, and any supplement thereto, will be passed upon by Cooley LLP. Additional legal matters may be passed upon for us or any underwriters, dealers or agents, by counsel that we will name in the applicable prospectus supplement. As of the date of this prospectus, GC&H Investments, LLC, an entity consisting of current and former partners and associates of Cooley LLP, beneficially holds an aggregate of 9,444 shares of our common stock.

EXPERTS

The consolidated financial statements of Kezar Life Sciences, Inc. as of December 31, 2018 and 2017, and for each of the years in the three-year period ended December 31, 2018, have been incorporated by reference herein in reliance upon the report of KPMG LLP, independent registered public accounting firm, incorporated by reference herein, and upon the authority of said firm as experts in accounting and auditing.

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WHERE YOU CAN FIND MORE INFORMATION

This prospectus is part of the registration statement on FormS-3 we filed with the SEC under the Securities Act. This prospectus does not contain all of the information set forth in the registration statement and the exhibits to the registration statement. For further information with respect to us and the securities we are offering under this prospectus, we refer you to the registration statement and the exhibits and schedules filed as a part of the registration statement. You should rely only on the information contained in this prospectus or incorporated by reference. We have not authorized anyone else to provide you with different information. We are not making an offer of these securities in any state where the offer is not permitted. You should not assume that the information in this prospectus is accurate as of any date other than the date on the front page of this prospectus, regardless of the time of delivery of this prospectus or any sale of the securities offered by this prospectus.

We file annual, quarterly and current reports, proxy statements and other information with the SEC. You may read and copy the registration statement, as well as any other document filed by us with the SEC, at the SEC’s Public Reference Room at 100 F Street NE, Washington, D.C. 20549. You can also request copies of these documents by writing to the SEC and paying a fee for the copying cost. You may obtain information on the operation of the Public Reference Room by calling the SEC at(800) SEC-0330. The SEC maintains a website that contains reports, proxy and information statements and other information regarding issuers that file electronically with the SEC, including Kezar. The address of the SEC website is www.sec.gov.

We maintain a website at www.kezarbio.com. Information contained in or accessible through our website does not constitute a part of this prospectus.

INCORPORATION OF CERTAIN INFORMATION BY REFERENCE

The SEC allows us to “incorporate by reference” information from other documents that we file with it, which means that we can disclose important information to you by referring you to those documents. The information incorporated by reference is considered to be part of this prospectus. Information in this prospectus supersedes information incorporated by reference that we filed with the SEC prior to the date of this prospectus. We incorporate by reference into this prospectus and the registration statement of which this prospectus is a part the information or documents listed below that we have filed with the SEC(File No. 001-38542):

∎ our Annual Report onForm 10-K for the fiscal year ended December 31, 2018, filed with the SEC on March 26, 2019;

∎ our definitive Proxy Statement onSchedule 14A, filed with the SEC on April 30, 2019 (excluding those portions that are not incorporated by reference into our Annual Report onForm 10-K for the fiscal year ended December 31, 2018);

∎ our Quarterly Report onForm 10-Q for the quarter ended March 31, 2019, filed with the SEC on May 7, 2019;

∎ our Current Reports onForm  8-K filed with the SEC onJanuary  8, 2019,March 6, 2019,June 13, 2019 andJune 25, 2019, in each case to the extent the information in such reports is filed and not furnished; and

∎ the description of our common stock contained in our registration statement onForm 8-A filed with the SEC on June 19, 2018, including any amendments or reports filed for the purposes of updating this description.

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Notwithstanding the statements in the preceding paragraphs, no document, report or exhibit (or portion of any of the foregoing) or any other information that we have “furnished” to the SEC pursuant to the Exchange Act shall be incorporated by reference into this prospectus.

We also incorporate by reference into this prospectus all documents (other than current reports furnished under Item 2.02 or Item 7.01 of Form8-K and exhibits filed on such form that are related to such items) that are filed by us with the SEC pursuant to Sections 13(a), 13(c), 14 or 15(d) of the Exchange Act (i) after the date of the initial filing of the registration statement of which this prospectus forms a part and prior to effectiveness of the registration statement, or (ii) after the date of this prospectus but prior to the termination of the offering. These documents include periodic reports, such as Annual Reports on Form10-K, Quarterly Reports on Form10-Q and Current Reports on Form8-K, as well as proxy statements.

We will provide to each person, including any beneficial owner, to whom a prospectus is delivered, without charge upon written or oral request, a copy of any or all of the documents that are incorporated by reference into this prospectus but not delivered with the prospectus, including exhibits that are specifically incorporated by reference into such documents. You should direct any requests for documents to Kezar Life Sciences, Inc., Attn: Marc Belsky, Secretary, 4000 Shoreline Court, Suite 300, South San Francisco, California 94080; telephone: (650)822-5600.

Any statement contained in a document incorporated or deemed to be incorporated by reference in this prospectus will be deemed modified, superseded or replaced for purposes of this prospectus to the extent that a statement contained in this prospectus modifies, supersedes or replaces such statement.

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16,115,385 Shares of Common Stock

Pre-Funded Warrants to Purchase 2,884,615 Shares of Common Stock

PROSPECTUS SUPPLEMENT

Joint Book-Running Managers

Cowen Wells Fargo Securities William Blair

January 31, 2020