The association between platelet count and the prognosis of patients with gastric cancer has already been reported by numerous studies. As the reports are inconsistent, we conducted this meta-analysis to evaluate the prognostic significance of platelet count in patients with gastric cancer. A comprehensive search was performed in PubMed, Embase, and the Cochrane Library to identify relevant studies, which evaluated the prognostic impact of pretreatment platelet count in patients with gastric cancer. Data was pooled using a random effect model to calculate hazard ratios (HRs) and odds ratios (ORs) with 95% confidence intervals (CIs). Around 10 studies were included, comprising 8166 patients in total. The result showed that patients with thrombocytosis had significant worse overall survival (HR 1.57, 95% CI 1.36-1.81, P < .001) than those with normal platelet count, and were associated with advanced clinical stage (OR, 1.57; 95% CI, 1.15-2.13; P = .004), deeper tumor invasion (OR,3.49; 95% CI, 2.48-4.91; P < .001), and higher risk of recurrence (OR, 2.28; 95% CI, 1.55-3.35; P < .001). Pretreatment thrombocytosis is a potential effective predictor of overall survival (OS) for patients with gastric cancer and is correlated with higher risks of recurrence, serosal invasion, and advanced stage.