PURPOSE: Metastatic castration-resistant prostate cancer (mCRPC) remains a significant therapeutic challenge and a leading cause of cancer-related mortality in men. PARP inhibitors like Olaparib are effective in homologous recombination repair (HRR)-deficient tumors, but resistance often arises through DNA repair restoration. This study explores the role of the structure-specific endonuclease subunit SLX1, a catalytic subunit of the SLX1-SLX4 endonuclease complex, in Olaparib resistance. METHODS: Data from The Cancer Genome Atlas (TCGA) were used for expression and survival analyses. The CRPC cell line DU145, which harbors BRCA1 and BRCA2 mutations, was used as a cell model for both in vitro and in vivo studies. RESULTS: Elevated SLX1A expression in prostate cancer tissues was associated with significantly reduced progression-free and overall survival. SLX1 protein was upregulated in androgen-resistant prostate cancer cell lines (DU145, 22RV1, PC3) and further increased in Olaparib-resistant DU145 (DU145-OR) cells. Silencing SLX1 via shRNA enhanced Olaparib sensitivity, reducing colony formation and increasing DNA damage and apoptosis in DU145 and DU145-OR cells. Mechanistically, SLX1 knockdown disrupted SLX4 interactions with critical DNA repair proteins (ERCC1-XPF, PLK1, and TOPBP1), impairing DNA repair complex stability. In vivo, SLX1-silenced DU145 xenografts treated with Olaparib showed significantly reduced tumor growth with decreased Ki-67 expression and increased apoptosis/necrosis compared to controls. CONCLUSION: This study highlights SLX1 as both a prognostic marker and potential therapeutic target to enhance PARPi efficacy in advanced prostate cancer. Targeting SLX1 may be a promising strategy to overcome Olaparib resistance in mCRPC patients with homologous recombination deficiency.