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Immunotherapy has shown promising efficacy in esophageal squamous cell carcinoma (ESCC), yet its clinical benefits remain limited due to immune evasion. Lactate accumulation in the tumor microenvironment has been found to facilitate immune evasion through protein lactylation. However, the key lactylated substrates and mechanisms driving immune evasion remain undefined. Here, we show that HSPA1A lactylation at lysine 108 (K108) by KAT5 drives CD8⁺ T cell dysfunction and immunotherapy resistance via the STAT1/PD-L1 axis in ESCC. Mechanistically, K108 lactylation enhances HSPA1A binding to STAT1, protecting STAT1 from TRIM25-mediated ubiquitination and proteasomal degradation. This stabilization promotes STAT1 phosphorylation and nuclear translocation, leading to transcriptional upregulation of PD-L1 and subsequent immune evasion. Collectively, these findings highlight the pivotal role of HSPA1A lactylation in facilitating immune evasion via the STAT1/PD-L1 axis, suggesting a potential target for improving immunotherapy efficacy in ESCC.