The benefit of immunochemotherapy employing a streptococcal preparation, OK-432 (Picibanil), in patients with curatively resected gastric cancer was reassessed by meta-analysis of data from 1,522 patients enrolled in six clinical trials with central randomization. All six trials began between 1985 and 1993, and patients were followed-up for at least 3 years after surgery and enrollment of the last patient. In these trials, standard chemotherapy was compared with the same chemotherapy plus OK-432. The endpoint was overall survival and intent-to-treat analysis was done without patient exclusion. Data were analyzed using the Mantel-Haenszel method. The 3-year survival rate for all eligible patients in the six trials was 67.5% in the immunochemotherapy group versus 62.6% in the chemotherapy group. The 3-year overall survival odds ratio was 0.81 (95% confidence interval: 0.65–0.99). The treatment effect was shown to be statistically significant (p = 0.044). The results of this meta-analysis suggest that immunochemotherapy after surgery with OK-432 can improve the survival of patients with curatively resected gastric cancer.