Background: This study aimed to confirm the prognostic role of pretreatment neutrophil to lymphocyte ratio (NLR), platelet to lymphocyte ratio (PLR), hemoglobin (Hb) levels as effective and convenient biomarkers for patients with advanced or metastatic gastric cancer (AGC or MGC) receiving immunotherapy. Methods: patients with AGC and MGC who received anti-PD-1 treatment at the Chinese PLA General Hospital between January 2016 and November 2020 were reviewed. The receiver operating characteristic analyses for predicting 6 months PFS by the NLR, PLR was used to identify an appropriate cut-off value. The study analyzed the association of NLR, PLR, Hb and overall survival (OS) or progression-free survival (PFS) and anti-tumor response rate with immunotherapy respectively. Results: 137 patients were included in the final analysis. 71 patients were administered immunotherapy in the first line and the rest of the patients in the second or further line. 92 patients had received immunotherapy combined with chemotherapy, whereas 45 patients had undertaken immunotherapy monotherapy or with anti-angiogenesis. The best cut-off value for NLR was 3.23 and for PLR was 816.43. NLR <3.23 was associated with longer OS (HR = 0.38, 95% CI, 0.26-0.57, p < 0.001) and PFS (HR = 0.42, 95% CI, 0.29-0.62, p < 0.001) in patients with AGC or MGC. Patients in PLR<816.43 group had prolonged PFS (7.9m vs 4.3m, p<0.001) and OS (11.1m vs9.2m, p<0.001) than in PLR>=816.43 group. The median PFS was 7.8m in the normal Hb level group (Hb>=110g/L) and 4.3m in the decreased Hb group (Hb<110g/L) (HR=0.5, 95% CI 0.31, 0.81, P=0.004). The OS was 14.4m with normal Hb level as compared with 8.2m with decreased Hb level( HR=0.59, 95% CI 0.37, 0.94, P=0.024). No significant difference was observed in objective response rate (ORR) and disease control rate (DCR) in the different NLR, PLR, Hb group, respectively. Univariate and multivariate analysis found that NLR, PLR, Hb were independent prognostic biomarkers for PFS and OS (p<0.05). Conclusions: pre-treatment NLR, PLR, Hb was significantly associated with PFS and OS in patients with AGC and MGC who received immunotherapy. Clinicians need to consider patients with elevated NLR and PLR or decreased Hb level for decisions on immunotherapy strategy.