We report a case of a 65-year-old male with stage IV gastric cancer accompanied by liver metastases, which showed a significant response after administration of TS-1. One hundred and twenty mg/body/day of TS-1 was orally administered without hospitalization. After 3 months, upper GI endoscopy showed improvement of primary gastric lesion, and cancer cells could not be detected under biopsy. After 2 months, computed tomography (CT) showed a reduction in the multiple liver metastases. Moreover, after 15 months, CT showed a complete regression of the multiple liver metastases, for a complete response (CR). The serum level of carcinoembryonic antigen (CEA) was reduced from 115 to within normal range. Noticeable critical adverse effects did not appear. Treatment on an outpatient basis, therefore, greatly contributed to his quality of life. We judged that TS-1 might be a candidate anti-cancer drug for first-line chemotherapy for advanced gastric cancer.