PARP inhibitor (PARPi) resistance presents a significant challenge in ovarian cancer treatment, necessitating the development of effective therapeutic strategies to overcome this resistance and improve patient outcomes. Our study demonstrated that elevated expression of SRY-box 9 (SOX9) contributes to olaparib resistance in ovarian cancer. Mechanistically, the deubiquitinating enzyme USP28 was identified as a novel interacting partner of SOX9. USP28 inhibited the ubiquitination and subsequent degradation of SOX9, which is mediated by the E3 ubiquitin ligase FBXW7 during olaparib treatment. ChIP-Seq analysis revealed that SOX9 binds to the promoters of key DNA damage repair (DDR) genes (SMARCA4, UIMC1, and SLX4), thereby regulating DDR processes in ovarian cancer. Additionally, USP28 promoted olaparib resistance by stabilizing SOX9 protein and enhancing DNA damage repair. Furthermore, the USP28 specific inhibitor AZ1 reduced SOX9 protein stability and increased the sensitivity of ovarian cancer cells to olaparib. In conclusion, targeted inhibition of USP28 promoted ubiquitination-mediated degradation of SOX9, thereby impairing DNA damage repair capabilities and sensitizing ovarian cancer cells to PARPi. These findings elucidate the underlying mechanisms of PARPi resistance in ovarian cancer and suggest the potential efficacy of combining USP28 inhibitors with PARPi to overcome this resistance.