Adjuvant chemotherapy with gemcitabine is the standard treatment in Japan for patients who have undergone resection of pancreatic cancer. However, few reports have described suitable regimens for patients who present cancer relapse following adjuvant chemotherapy. In the present study, we retrospectively evaluated the efficacy and safety of S-1, an oral fluoropyrimidine derivative, as a second-line chemotherapy for patients who had suffered relapse of pancreatic cancer following adjuvant chemotherapy with gemcitabine. A total of 51 patients with pancreatic cancer suffered relapse after curative resection and subsequent adjuvant chemotherapy with gemcitabine at our institution. A group of 26 of these patients were administered S-1 orally twice daily after meals at a dose of 80 mg/m(2) for body surface areas for 14 consecutive days, followed by a 7-day rest (S-1 group). The remaining 25 patients received no additional anticancer drugs other than continuation of gemcitabine (GEM/BSC group). During a median follow-up period of 35 months, a significant difference was observed in overall survival (OAS) between the S-1 group and the control group (median OAS, 20.9 vs. 13.7 months; p=0.0157, log-rank test). Furthermore, there was a significant inter-group difference in survival after relapse (SAR) (median SAR, 11.4 vs. 6.20 months; p=0.0025, log-rank test). No increase in grade 3/4 hematological and non-hematological toxicity was observed in the S-1 group. In conclusion, second-line chemotherapy using a combination of S-1 and adjuvant chemotherapy with gemcitabine may be an efficient and beneficial strategy for patients with relapsed pancreatic cancer.