Abstract Background Sarcopenia is a syndrome characterized by progressive and generalized loss of skeletal muscle mass and strength. This study aims to explore the prevalence of sarcopenia in overweight and obese gastric cancer (GC) patients and figured out the impacts of sarcopenia on the postoperative complication of overweight and obese GC patients. Methods According to the recommended body-mass index (BMI) for Asian populations by WHO, we conducted a prospective study of overweight and obese gastric cancer patients (BMI ≥ 23kg/m2 ) under curative gastrectomy from August 2014 to December 2015. Including lumbar skeletal muscle index, handgrip strength and gait speed as the sarcopenic components were measured before surgery. Patients were followed up after gastrectomy to gain the actual clinical outcomes. Factors contributing to postoperative complications were analyzed by univariate and multivariate analysis. Results Total of 206 overweight or obese patients were enrolled in this study, 14 patients were diagnosed sarcopenia and were demonstrated having significantly association with higher risk of postoperative complications, higher hospital costs, and higher rate of 30-days readmission compared with the non-sarcopenic ones. On the basis of univariate and multivariate analysis, sarcopenia was an independent risk factor for postoperative complication of overweight and obese patients with gastric cancer ( P = 0.002). Conclusion Sarcopenia is an independent predictor of postoperative complications in overweight or obese patients with gastric cancer after radical gastrectomy.