Objective: Malnutrition, which is frequently seen in patients with gastrointestinal system cancer; affects prognosis, quality of life, and survival. In this study, the prognostic value of the Prognostic Nutritional Index (PNI) and Geriatric Nutritional Risk Index (GNRI) based on malnutrition and systemic inflammatory response were compared to determine which index was more predictive for survival. Material and Methods: A total of 124 patients were included in the study. Statistical analysis was done with SPSS program. Kaplan-Meier analysis and Log-Rank test were used for survival analysis. Factors affecting overall survival (OS) were analyzed with univariate and multivariate Cox regression analysis. The values of the indices in predicting the cutoff point and OS were recorded by calculating area under the curve by receiver operating characteristic analysis. Results: In univariate analysis; primary tumor location at the cardioesophageal junction, increased CRP, decreased lymphocyte count, and low PNI (≤44.05) significantly decreased OS (p<0.05). Only the primary tumor location at the cardioesophageal junction was an independent prognostic factor for mortality (hazard ratio: 2.717; 95% confidence interval: 1.292-5.711; p=0.008). Conclusion: Although PNI is not an independent risk factor for OS in patients with metastatic gastric cancer, it can be an indicator of survival. In addition, PNI was found to be a better prognostic marker in predicting OS than GNRI.