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Background: Immune checkpoint inhibitors (ICI) have shown promising prospects in gastroesophageal junction (G/GEJ) cancer immunotherapy, many clinical trials have been carried out. Objective: To evaluate the efficacy and safety of ICI in G/GEJ cancer. Methods: The published English articles of PubMed, Cochrane Library, Embase, Web of Science were searched up to 30/09/2018. The efficacy and safety of ICI were analyzed by meta-analysis. Results: A total of 2003 patients from nine clinical trials were included. Anti-PD-1 treatment improved the 12-month, 18-month overall survival (OS) rate (RR, 1.79 p = 0.013; 2.20 p = 0.011) and prolonged the duration of response (DOR) (MSR, 3.27 p < 0.001). The objective response rate (ORR) in PD-L1+ patients was greater than PD-L1− (RR, 4.31 p < 0.001). Microsatellite instability-high (MSI-H) patients had higher ORR and disease control rate (DCR) than microsatellite stability (MSS) (RR, 3.40 p< 0.001; 2.26 p= 0.001). The most common grade ≥3 treatment-related adverse events (TRAEs) were fatigue, aspartate aminotransferase increased, hepatitis, pneumonitis, colitis, hypopituitarism. The TRAE incidence of anti-PD-1/PD-L1 was less than chemotherapy (TRAE RR = 0.64 p< 0.001; ≥3 TRAE RR = 0.37 p < 0.001). The incidence of ≥3 TRAEs of anti-PD-1/PD-L1 treatment was less than that of anti-CTLA-4 (11.7% vs 43.9%). Conclusions: ICI treatment could improve some but not all survival endpoints to advanced or metastatic G/GEJ cancer patients suggesting modest benefit and less adverse reactions. Anti-PD-1/PD-L1 therapy was more effective to PD-L1+, MSI-H, EBV+, or high tumor mutational burden patients. [ABSTRACT FROM AUTHOR]