The results of the Adjuvant Chemotherapy Trial of S-1 for Gastric Cancer(ACTS-GC)demonstrated that postoperative chemotherapy using S-1 is a standard treatment in Japan for patients with p-Stage II and p-Stage III gastric cancer. We retrospectively reviewed the effect of adjuvant chemotherapy received by 47 patients with p-Stage II and p-Stage III gastric cancer between January 2007 and June 2012. Our hospital is a local university hospital with a high intensive care unit. S-1 monotherapy was administered to 32 patients(adjuvant S-1 group, 68.1%); 22 patients(68.8%)among them completed one year of therapy without any modification to the administration schedule. A total of 8 patients(25.0%)experienced grade 3 adverse events, and 9 patients required a dose reduction, a modification of the administration schedule, or termination of the therapy. S-1 was not administrated to 15 patients(no adjuvant S-1 group, 31.9%); among these patients, 12(80.0%) were not administered S-1 because of their advanced age and comorbidity. The 3-year overall survival rate was 89.3% in the adjuvant S-1 group and 77.1% in the no adjuvant S-1 group. The completion rate of S-1 and survival rate were high for patients in the adjuvant S-1 group, which was similar to the results of the ACTS-GC. However, 25 of 47 patients(53.2%) with p-Stage II and p-Stage III gastric cancer did not improve after sufficient adjuvant therapy; therefore, it is important to develop new treatment strategies for these patients.