Background: The impact of sex chromosomes on the tumor microenvironment (TME) is significant, beyond hormonal effects. This study investigates the role of the sex-determining gene SRY in the immune microenvironment of hepatocellular carcinoma (HCC), focusing on how SRY regulates immune checkpoints and contributes to gender disparities in immunotherapy response. Methods: Multiple HCC mouse models (chemically induced, hydrodynamic, orthotopic, subcutaneous) using SRY transgenic knockout (KO) or knock-in (KI) mice were employed. To eliminate hormonal effects, the mice were castrated. Flow cytometry, immunofluorescence, and ELISA assessed T cell changes in the TME. Cellular models used PCR array, CUT&Tag, qPCR, WB, and luciferase assays to explore SRY's transcriptional regulation. Clinical samples validated correlations between SRY, immune markers, and PD-L1. Results: •In castrated male SRY-KO mice, increased CD8 + T cells and elevated GZMB, TNF-alpha, and IFN-gamma were observed in the TME.•SRY-KI in castrated males reduced CD8 + T cells and functional markers.•Ectopic SRY in castrated females similarly impaired T cell infiltration and function.•PCR array in SRY-overexpressing HCC cells revealed upregulation of PD-L1.•CUT&Tag and luciferase assays confirmed SRY binds the IRF1 promoter, upregulating IRF1 expression.•IRF1 knockdown abolished PD-L1 upregulation, confirming an SRY-IRF1-PD-L1 axis.•In vivo, PD-L1 knockdown in SRY-overexpressing tumors reversed immune suppression and tumor growth.•Anti-PD-L1 treatment showed enhanced efficacy in SRY-overexpressing tumors.•Clinical HCC samples confirmed positive SRY-PD-L1 correlation and negative SRY-CD8 + T cell correlation. Conclusions: SRY, a male-specific gene, regulates the immune checkpoint PD-L1 via IRF1, suppressing CD8 + T cell function in the TME. Targeting the SRY-IRF1-PD-L1 axis may improve immunotherapy outcomes, especially in male HCC patients. The text has been translated and polished using AI.