Objective:To analyze the significance of systemic immune inflammatory index (SII) combined with neutrophil lymphocyte ratio (NLR) in the treatment of advanced gastric cancer with PD-1/PD-L1 inhibitors.Methods:The clinical data of 90 patients with stage Ⅳ gastric adenocarcinoma who received immunotherapy from January 2020 to January 2023 were retrospectively analyzed, including 70 males and 20 females, aged from 36 to 80 years, with an average age of (53.76±15.58) years. The clinicopathological features and follow-up data were collected. SPSS 26.0 software was used to conduct statistical analysis. The critical values of NLR, SII, PLR and MLR were calculated, and the overall survival (OS) and progression free survival (PFS) of patients with different levels of markers were analyzed. The independent predictive factors of PFS and OS were determined, and the predictive value of risk factors for PFS and OS in patients with gastric cancer was evaluated.Results:The median follow-up time of all patients was 27.3 months, and the median PFS and OS were 10.0 months and 17.7 months, respectively. The area under the curve (AUC) of NLR and SII for predicting PFS and OS were>0.7, the critical values NLR were 4.75 and 3.85, and SII were 1154.67 and 887.90, respectively. PFS and OS in patients with high NLR, high MLR, high PLR and high SII were lower than those in patients with low levels. ECoG PS≥ 1, high NLR and high SII were independent influencing factors of disease progression or death. The AUC of the combination of NLR, ECoG PS and SII was 0.761, which was higher than that of any single factor. The fewer the number of risk factors, the longer the PFS and OS.Conclusions:NLR and SII are effective predictors of PFS and OS in patients with advanced gastric cancer receiving immunotherapy. Pre treatment detection of NLR and SII can provide reliable guidance for immunotherapy of advanced gastric cancer.