OBJECTIVE: This study aims to elucidate the relationship between postoperative monocyte count and gastric cancer prognosis. We introduce a standardized monocyte ratio (MMR) to predict postoperative survival rates in gastric cancer patients effectively. METHODS: A test cohort was created to develop and evaluate the pre- and postoperative MMR as a mortality predictor in gastric cancer patients. We used Kaplan-Meier survival analysis, complemented by univariate and multivariate analyses. The predictive utility of MMR was assessed via time-dependent ROC curves and decision-curve analysis. RESULTS: The sample distributions in both cohorts were similar. The MMR showed high predictive value and significant clinical benefits in 1, 3, and 5-year overall survival (OS) assessments. These findings enhance understanding of prognosis and aid in developing more precise treatment plans. CONCLUSIONS: MMR is confirmed as an independent factor in predicting overall survival in gastric cancer patients, proving to be a reliable and cost-effective prognostic indicator.