The 2024 Special Meeting of Stockholders (the “Special Meeting”) of Oaktree Specialty Lending Corporation, a Delaware corporation (the “Company”), will be conducted online on March 4, 2024, at 10:30 a.m., Pacific Time (1:30 p.m., Eastern Time), at the following website: www.virtualshareholdermeeting.com/ocsl2024sm.

At the Special Meeting, the Company’s stockholders will consider and vote on a proposal to authorize the Company, with the approval of the Board of Directors, to sell or otherwise issue shares of its common stock at a price below its then current net asset value per share, provided that the number of shares issued does not exceed 25% of its then outstanding common stock.

THE BOARD OF DIRECTORS, INCLUDING ALL OF THE INDEPENDENT DIRECTORS, RECOMMENDS THAT YOU VOTE “FOR” THE PROPOSAL DESCRIBED IN THE ACCOMPANYING PROXY STATEMENT.

You have the right to receive notice of, and to vote at, the Special Meeting if you were a stockholder of record at the close of business on January 4, 2024. A proxy statement is attached to this Notice that describes the matter to be voted upon at the Special Meeting or any adjournment(s) or postponement(s) thereof. The enclosed proxy card will instruct you as to how you may vote your proxy via the Internet, by telephone or by signing, dating and returning the enclosed proxy card.

Whether or not you plan to participate in the Special Meeting, we encourage you to vote your shares by following the instructions on the enclosed proxy card. Please note, however, that if you wish to vote during the Special Meeting and your shares are held of record by a broker, bank, trustee or nominee, you must obtain a “legal” proxy issued in your name from that record holder.

We are not aware of any other business that may properly be brought before the Special Meeting.

Thank you for your continued support of the Company.

The Special Meeting will be a completely virtual meeting. There will be no physical meeting location and the meeting will only be conducted via live webcast. The Special Meeting will be held on March 4, 2024 at 10:30 a.m., Pacific Time (1:30 p.m., Eastern Time). To participate in the Special Meeting, visit www.virtualshareholdermeeting.com/ocsl2024sm and enter thecontrol number included on the enclosed proxy card or in the instructions that accompanied your proxy materials. Onlinewill begin at 10:20 a.m., Pacific Time (1:20 p.m., Eastern Time). Please allow time for onlineprocedures.

You are entitled to participate in the Special Meeting only if you are a stockholder of the Company as of the close of business on the record date for the Special Meeting, which is January 4, 2024 (the “Record Date”), or you hold a valid proxy for the Special Meeting.

This proxy statement is also available at https://www.oaktreespecialtylending.com.

In addition to transacting such other business as may properly come before the Special Meeting and any adjournments or postponements, at the Special Meeting, the Company’s stockholders will be asked to approve a proposal to authorize the Company, with the approval of the Board, to sell or otherwise issue shares of its common stock at a price below its then current net asset value (“NAV”) per share, provided that the number of shares issued does not exceed 25% of its then outstanding common stock (the “Proposal”).

The Chairman of the Company shall have the power to adjourn the Special Meeting, whether or not a quorum is present, from time to time for any reason and without notice other than announcement at the Special Meeting.

Beneficial ownership is determined in accordance with the rules of the Securities and Exchange Commission (“SEC”) and includes voting or investment power with respect to the securities. Ownership information for those persons who beneficially own 5% or more of the shares of the Company’s common stock is based upon filings by such persons with the SEC and other information obtained from such persons, if available.

Unless otherwise indicated, the Company believes that each beneficial owner set forth in the table below has sole voting and investment power over the shares beneficially owned by such beneficial owner. The directors are divided into two groups — interested director and independent directors. The interested director is an “interested person” of the Company as defined in Section 2(a)(19) of the 1940 Act. The address of all executive officers and directors is c/o Oaktree Specialty Lending Corporation, 333 South Grand Avenue, 28th Floor, Los Angeles, CA 90071.

The Company is ainvestment company that has elected to be regulated as a business development company (“BDC”) under the 1940 Act. As a BDC, the Company is generally prohibited from issuing shares of its common stock at a price below the then-current NAV per share unless the Company meets certain conditions, including obtaining stockholder approval. As a result, the Company is seeking the approval of its stockholders so that it may, in one or more public or private offerings of its common stock, sell or otherwise issue shares of its common stock at a price below its then current NAV per share, provided that the number of shares issued does not exceed 25% of its then outstanding common stock and subject to the conditions set forth in this Proposal. If this Proposal is approved by the Company’s stockholders, the authorization would be effective for common stock issued during a twelve-month period following such approval. The authorization would include offerings in connection with acquisitions of other companies or investment portfolios.

The Board, including all of the directors who have no financial interest in the Proposal and all of the directors who are not “interested persons” of the Company as defined in Section 2(a)(19) of the 1940 Act, has approved the Proposal as in the best interests of the Company and its stockholders and recommends it to the stockholders for their approval. For these purposes, directors are not deemed to have a financial interest solely by reason of their ownership of the Company’s common stock. The Board believes that having the flexibility to sell or otherwise issue common stock below its then current NAV per share in certain instances is in the Company’s best interests and the best interests of its stockholders. This would, among other things, provide access to the capital markets to take advantage of attractive investment and acquisition opportunities during periods of market dislocation or volatility and to add financial flexibility to comply with regulatory requirements and debt facility covenants, including any applicable asset coverage ratios. In addition, the Board noted that certain ratings agencies view stockholder authorization to issue shares of common stock below its then current NAV per share favorably. Upon obtaining the requisite stockholder approval, the Company will comply with the conditions described in this proxy statement in connection with any issuance undertaken pursuant to such authorization. A discussion of the risks of dilution appears below.

However, BDCs as an industry historically have traded below NAV and, in particular, shares of the Company’s common stock have traded below NAV. Although shares of the Company’s common stock traded at prices above NAV during portions of the 2023 fiscal year, there can be no assurance that they will trade at prices above NAV in the near term or that the premium at which shares of the Company’s common stock may trade in the future will be sufficiently large for the Company to issue shares in an offering above the then current NAV per share after taking into account the discounts, commissions or fees of any underwriter, dealer or agent in connection with such offering. If the current period of market dislocation and volatility continues or another period of market dislocation and volatility were to occur, the Company may not have access to sufficient debt and equity capital in order to take advantage of attractive investment and acquisition opportunities that are created during such period. In addition, the debt capital that will be available, if any, may be at a higher cost and

In addition, failure to maintain the asset coverage required by the 1940 Act or by any debt facility could have severe negative consequences for the Company, including the inability to pay dividends and breach of debt covenants. Although the Company is in compliance with, and does not currently expect that it will breach, the allowable asset coverage ratios, the markets it operates in and the general economy have experienced volatility in the past and may become volatile again in the future. Even if the underlying performance of one or more portfolio companies may not indicate an impairment or inability to repay all principal and interest in full, volatility in the capital markets may negatively impact the valuations of investments and create unrealized capital depreciation on certain investments. Any such write-downs in value (as well as unrealized capital depreciation based on the underlying performance of the Company’s portfolio companies, if any) will negatively impact the Company’s total assets and the resulting asset coverage ratio. Issuing additional equity would allow the Company to realign its asset coverage ratio and avoid these negative consequences. In addition to meeting legal requirements applicable to BDCs, having a more favorable asset coverage and debt to equity ratio would also generally strengthen the Company’s balance sheet, potentially improve access to the debt markets and provide greater flexibility for the Company to fully execute its business strategy.

The Board believes that having the flexibility to issue common stock below NAV per share in certain instances is in the best interests of the Company and its stockholders. During volatile periods, such as the current market environment, this would, among other things, provide access to capital markets to pursue attractive investment and acquisition opportunities and add financial flexibility to comply with regulatory requirements and debt facility covenants, including the applicable asset coverage ratios. It could also minimize the likelihood that the Company would be required to sell assets that the Company would not otherwise sell, which sales could occur at times and at prices that are disadvantageous to the Company and its stockholders.

While the Company has no immediate plans to issue any shares of its common stock below NAV, it is seeking stockholder approval now in order to provide flexibility if it desires in the future to issue shares of its common stock below NAV per share, which typically must be undertaken quickly. The final terms of any such sale will be determined by the Board at the time of issuance, and the shares of common stock will not include

The following table illustrates the dilutive and accretive effect in the hypothetical 25% discount offering from the prior chart for Stockholder A that acquires shares equal to (1) 50% of their proportionate share of the offering (i.e., 1,250 shares, which is 0.50% of the offering of 250,000 shares rather than their 1.00% proportionate share) and (2) 150% of their proportionate share of the offering (i.e., 3,750 shares, which is 1.50% of the offering of 250,000 shares rather than their 1.00% proportionate share). The prospectus pursuant to which any discounted offering is made will include a chart for these examples based on the actual number of shares in such offering and the actual discount from the most recently determined NAV. It is not possible to predict the level of market price decline that may occur. These examples are provided for illustrative purposes only.

The following table illustrates the dilutive and accretive effects on Stockholder A who purchases the same percentage (1.00%) of the shares in three hypothetical offerings of common stock of different sizes and levels of discount from NAV: (1) an offering of 50,000 shares (5% of the outstanding shares) at $9.50 per share after offering expenses and commissions (a 5% discount from NAV); (2) an offering of 100,000 shares (10% of the outstanding shares) at $9.00 per share after offering expenses and commissions (a 10% discount from NAV); (3) an offering of 250,000 shares (25% of the outstanding shares) at $7.50 per share after offering expenses and commissions (a 25% discount from NAV); and (4) an offering of 250,000 shares (25% of the outstanding shares) at $0.00 per share after offering expenses and commissions (a 100% discount from NAV). The prospectus pursuant to which any discounted offering is made will include a chart for these examples based on the actual number of shares in such offering and the actual discount from the most recently determined NAV. It is not possible to predict the level of market price decline that may occur. These examples are provided for illustrative purposes only.

The 1940 Act establishes a connection between market price and NAV per share because, when common stock is sold or otherwise issued at a sale price below NAV per share, the resulting increase in the number of outstanding shares is not accompanied by a proportionate increase in the net assets of the issuer. The Board will consider the potential dilutive effect of the issuance of shares of common stock at a price below NAV per share when considering whether to authorize any such issuance pursuant to the stockholder approval being sought here.

Stockholders should also consider that they will have no subscription, preferential or preemptive rights to additional shares of the common stock proposed to be authorized for issuance pursuant to the Proposal, and thus any future issuance of common stock at a price below NAV per share will dilute such stockholders’ holdings of common stock as a percentage of shares outstanding to the extent such stockholders do not purchase sufficient shares of common stock in the offering or otherwise to maintain their percentage interest. Further, if current stockholders of the Company do not purchase any shares of common stock to maintain their percentage interest, regardless of whether such offering is above or below the then current NAV per share, their voting power will be diluted.

As discussed above, it should be noted that the maximum number of shares of common stock issuable below NAV per share that could result in such dilution is limited to 25% of the Company’s then outstanding common stock.

We will furnish, without charge, a copy of our Annual Report on Formfor the fiscal year ended September 30, 2023 to any stockholder upon request. Requests should be directed to Oaktree Specialty Lending Corporation, 1301 Avenue of the Americas, 34th Floor, New York, NY 10019, by telephone at (212)or byat

Any stockholder proposals submitted pursuantSecurities Exchange Act of 1934, as amended (the “Exchange Act”) for inclusion in the Company’s proxy statement and form of proxy for the 2025 annual meeting of stockholders must be received by the Company on or before September 21, 2024. Such proposals must also comply with the requirements as to form and substance established by the SEC if such proposals are to be included in the proxy statement and form of proxy. Any such proposal should be mailed to: Oaktree Specialty Lending Corporation, 333 South Grand Avenue, 28th Floor, Los Angeles, CA 90071, Attention: Secretary. Proxies solicited by the Company will confer discretionary voting authority with respect to these proposals, subject to SEC rules governing the exercise of this authority.

Stockholder proposals or director nominations to be presented at an annual meeting of stockholders, other than stockholder proposals submitted pursuantthe Exchange Act, must be delivered to, or mailed and received at, the principal executive offices of the Company not more than 150 days and not less than 120 days prior to the date of the anniversary of the previous year’s annual meeting of stockholders. For the 2025 annual meeting of the Company’s stockholders, the Company must receive such proposals and nominations no earlier than October 5, 2024 and no later than November 4, 2024. If the annual meeting of stockholders is scheduled to be held on a date more than 30 days prior to or after such anniversary date, stockholder proposals or director nominations must be received no later than the 10th day following the day on which such notice of the date of the 2025 annual meeting of stockholders was mailed or such public disclosure of the date of the annual meeting was made. Proposals and nominations must also comply with the other requirements contained in the Company’s bylaws, including supporting documentation and other information and representations.

The Board does not presently intend to bring any other business before the Special Meeting. As to any other business that may properly come before the Special Meeting, however, proxies will be voted in respect thereof in accordance with the discretion of the proxyholders.

Whether or not you expect to participate in the Special Meeting, please follow the instructions provided on the enclosed proxy card or in the instructions that accompanied your proxy materials to vote via the Internet, by telephone, or by signing, dating and returning the enclosed proxy card so that you may be represented at the Special Meeting. The Special Meeting will be a completely virtual meeting of stockholders and will be conducted exclusively by webcast. To participate in the Special Meeting, visit www.virtualshareholdermeeting.com/ocsl2024sm and enter thecontrol number included on the enclosed proxy card or in the instructions that accompanied your proxy materials. Onlinewill begin at 10:20 a.m., Pacific Time (1:20 p.m., Eastern Time). Please allow time for onlineprocedures. For questions regarding the Special Meeting and voting, please contact the Company by calling collect atbyator by writing to Oaktree Specialty Lending Corporation, 333 South Grand Avenue, 28th Floor, Los Angeles, CA 90071, Attention: Secretary.

Please note that only one copy of this proxy statement or Notice of Virtual Special Meeting may be delivered to two or more stockholders of record of the Company who share an address unless we have received contrary instructions from one or more of such stockholders. We will deliver promptly, upon request, a separate copy of any of these documents to stockholders of record at a shared address to which a single copy of such document(s) was delivered. Stockholders who wish to receive a separate copy of any of these documents, or to receive a single copy of such documents if multiple copies were delivered, now or in the future, should submit their request by calling us collect at (213)or by writing to Oaktree Specialty Lending Corporation, 333 South Grand Avenue, 28th Floor, Los Angeles, CA 90071, Attention: Secretary.

The principal address of Oaktree Fund Advisors, LLC, the Company’s investment adviser, and Oaktree Administrator is 333 South Grand Avenue, 28th Floor, Los Angeles, CA 90071.

The Company files periodic reports, current reports, proxy statements and other information with the SEC. This information is available on the SEC’s website at www.sec.gov. This information, including the Company’s most recent Annual Report on Formis also available free of charge by calling us collect at (213)byator by writing to Oaktree Specialty Lending Corporation, 333 South Grand Avenue, 28th Floor, Los Angeles, CA 90071, Attention: Secretary, or on our website at https://www.oaktreespecialtylending.com. The information on our website is not incorporated by reference into this proxy statement.