| Cover Page | 3 Months Ended |
| Mar. 31, 2022 shares | |
| Cover [Abstract] | |
| Document Type | 10-Q/A |
| Amendment Flag | true |
| Amendment Description | F-star Therapeutics, Inc. (“F-star”, “our” or “we”) is filing this Amendment No. 1 on Form 10-Q/A (this “Amendment”) to its Quarterly Report on Form 10-Q for the fiscal quarter ended March 31, 2022 (the “Original Form 10-Q”), which was filed with the Securities and Exchange Commission on May 10, 2022. This Amendment replaces in its entirety Part I, Item 4 “Controls and Procedures” (“Item 4”) of the Original Form 10-Q, which inadvertently did not include the conclusion by our Chief Executive Officer and Chief Financial Officer of the effectiveness of our disclosure controls and procedures, as required by Item 307 of Regulation S-K. The new Item 4 provided by this Amendment includes a statement regarding the conclusion of our Chief Executive Officer and Chief Financial Officer that our disclosure controls and procedures were effective as of March 31, 2022. This Amendment does not amend the Original Form 10-Q in any other way. Specifically, it does not update the Original Form 10-Q to reflect events occurring after May 10, 2022. |
| Document Period End Date | Mar. 31, 2022 |
| Document Fiscal Year Focus | 2022 |
| Document Fiscal Period Focus | Q1 |
| Trading Symbol | FSTX |
| Title of 12(b) Security | Common Stock, $0.0001 par value per share |
| Security Exchange Name | NASDAQ |
| Entity Registrant Name | F-STAR THERAPEUTICS, INC. |
| Entity Central Index Key | 0001566373 |
| Current Fiscal Year End Date | --12-31 |
| Entity Current Reporting Status | Yes |
| Entity Interactive Data Current | Yes |
| Entity Filer Category | Non-accelerated Filer |
| Entity Small Business | true |
| Entity Emerging Growth Company | false |
| Entity Shell Company | false |
| Document Quarterly Report | true |
| Document Transition Report | false |
| Entity File Number | 001-37718 |
| Entity Incorporation, State or Country Code | DE |
| Entity Tax Identification Number | 52-2386345 |
| Entity Address, Address Line One | Eddeva B920 Babraham Research Campus |
| Entity Address, City or Town | Cambridge |
| Entity Address, Postal Zip Code | CB22 3AT |
| Entity Address, Country | GB |
| City Area Code | 44 |
| Local Phone Number | 1223-497400 |
| Entity Common Stock, Shares Outstanding | 21,493,212 |
