Abstract: In recent years, there has been significant progress in the application of immunotherapy for advanced gastric cancer (AGC). Novel treatment approaches such as immune checkpoint inhibitors (ICIs) have shown promising efficacy, but not all patients benefit from these treatments. Studies have shown that the effectiveness of immunotherapy is associated with various biomarkers, such as programmed cell death ligand 1 (PD-L1) expression, microsatellite instability (MSI), and tumor mutational burden (TMB). This review aims to summarize the research progress of immunotherapy-related biomarkers in AGC and explore future research directions.