Background Immune checkpoint inhibitors (ICIs) has shown remarkable benefit in the treatment of a range of cancer types, although it may initiate immune related adverse events (irAEs) in patients. Some studies have shown that there is a close relationship between the occurrence of irAEs and prognosis. In present study, we have attempted to establish whether the occurrence of irAEs after the use of anti PD-1 antibodies is associated with treatment efficacy in people with advanced gastric cancer (AGC). Methods This study included patients treated with the anti-PD-1 antibodies for AGC patients at The Fourth Hospital of Hebei Medical University. IrAEs were identified clinically and graded as per the National Cancer Institute Common Terminology Criteria for Adverse Events ver. 4.03. Efficacy was evaluated with objective response rate (ORR), disease control rate (DCR), progression free survival (PFS) and overall survival (OS). The analysis was performed to determine the association between irAEs and clinical outcomes. Result Of the 74 AGC patients in our study, 24 developed irAEs. The DCR of the irAE displayed a trend better than that of non-irAE group but without statistical difference (41.70% VS 6.0%, p = 0.118). Median PFS in the irAE group was superior to that in the non-irAE group (176 days VS 94 days, p = 0.001). Median OS also showed this trend of difference at borderline statistical level (292 days VS 239 days, p = 0.057). Multivariate analysis also demonstrated irAE (HR = 0.269, 95%CI: 0.088 to 0.822, p = 0.021) were associated independently with the better prognosis for AGC patients. Conclusion In advanced gastric cancer treated with anti PD-1 antibodies, the occourence of irAEs might contribute to the improved prognosis.