Background: Several studies have reported that postoperative complications such as anastomotic leakage affect long-term prognosis after gastric cancer surgery. This study aimed to determine whether or not long-term outcomes were affected by the postoperative inflammatory complications in patients who underwent curative resection for gastric cancer. Methods: The patients were retrospectively selected from the medical records of consecutive patients who underwent curative gastrectomy with nodal dissection for gastric cancer at Yokohama City University and Kanagawa Cancer Center from January 2000 to August 2015. Inflammatory complications were evaluated according to the Clavien-Dindo classification. Overall survival (OS) was compared between postoperative inflammatory complications (IC) and no-complication (NC) groups. Results: A total of 2,254 patients were eligible for inclusion in the present study. One hundred seventy-five patients had IC group, while 2,079 patients had not. Operation time (p < 0.001), blood loss (p < 0.001) was significantly greater in the IC group. The incidence of postoperative inflammatory complication grade 2 or higher was 8.5% in which, pancreatic fistula (2.8%), anastomotic leakage (1.8%) were occurred. The mortality rate was 0.18%. The five-year OS rates of the IC and NC groups were 74.9% and 83.2%, respectively. The difference was statistically significant (p = 0.015). Multivariate Cox’s proportional hazard analyses demonstrated that the postoperative inflammatory complications were a significant prognostic factor for OS. Conclusions: Postoperative inflammatory complications have an obvious impact on the OS in curatively resected gastric cancer patients. It is necessary to reduce the incidence of postoperative complications.