Background: Several studies have shown that postoperative infectious complications correlate with poor prognosis in various malignancies, but the prognostic significance of the postoperative inflammatory response in patients with gastric cancer remains unclear. The aim of study was to examine whether the systemic inflammatory response present in the early phase of the postoperative state correlates with long-term outcomes and to identify markers in patients with advanced gastric cancer. We evaluated C-reactive protein (CRP) and white blood cell (WBC) count as simple and versatile markers of postoperative systemic inflammation in clinical practice that may be suitable for detecting the magnitude of inflammatory reaction. Methods: This study retrospectively reviewed 444 patients who underwent radical gastrectomy for stage II/III gastric cancer. We evaluated maximum serum C-reactive protein (CRPmax) and white blood cell count (WBCmax), defined as the maximum serum CRP level and maximum WBC count during the interval from surgery until discharge, as systemic inflammation markers. Results: In univariate analyses, CRPmax, WBCmax and infectious complications were significantly associated with both overall survival (OS) (p<0.001, p<0.001 and p=0.011, respectively) and relapse-free survival (RFS) (p<0.001, p=0.001 and p<0.001, respectively). Multivariate analysis revealed that high CRPmax (>9.2 mg/dL) was an independent prognostic factor for OS (hazard ratio (HR) 1.69, 95% confidence interval (CI) 1.18–2.42, p=0.004) and RFS (HR 1.42, 95%CI 1.02–1.98, p=0.038), while WBCmax and infectious complications were not. Regarding the pattern of recurrence, hematogenous recurrence was significantly more frequent in the high-CRPmax group (16.7%) than in the low-CRPmax group (3.8%, p<0.001). Conclusions: CRPmax, which reflects the magnitude of systemic inflammation induced by surgical stress and postoperative complications in the early phase after surgery, may be a promising prognostic indicator in patients with stage II/III gastric cancer who undergo curative resection.