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Objective: Currently, there is an urgent need to identify immunotherapeutic biomarkers to increase the benefit of immune checkpoint inhibitors (ICIs) for patients with gastric cancer (GC). Homologous recombination deficiency (HRD) can modify the tumor immune microenvironment by increasing the presence of tumor-infiltrating lymphocytes and therefore might serve as a biomarker of immunotherapeutic response. We aimed to analyze the mutational pattern of HR-associated genes in Chinese patients with GC and its relevance to the tumor immune profile and clinical immunotherapeutic response. Methods: A panel of 543 cancer-associated genes was used to analyze genomic profiles in a cohort comprising 484 Chinese patients with GC. Correlations between HR gene mutations and tumor immunity or clinical outcomes were identifiedviabioinformatic analysis using 2 GC genomic datasets (TCGA and MSK-IMPACT). Results: Fifty-one of the 484 (10.54％) patients carried at least one somatic mutation in an HR gene;ATM (16/484, 3.31％) was among the most frequently mutated HR genes in the Chinese cohort. Mutations in HR genes were associated with elevated tumor mutational burden, enhanced immune activity, and microsatellite instability status. In the MSK-IMPACT cohort comprising 49 patients with stomach adenocarcinoma or gastroesophageal junction adenocarcinoma treated with ICIs, patients with HR-mut GC (n = 12) had significantly better overall survival than those with HR-wt GC (n = 37) (log-rank test,P < 0.05). Conclusions: Our data suggest that detection of somatic mutations in HR genes might aid in identifying patients who might benefit from immune checkpoint blockade therapy.