A 42-year-old female patient underwent total gastrectomy for gastric cancer (Borrmann's Type 3). Many rice-grain sized peritoneal metastases were observed in the transverse colon and mesenterium. The lesion was diagnosed as stage IV cancer and the degree of radical cure was determined to be C. Chemotherapy with TS-1 was administered postoperatively. In each cycle, the drug was administered at a daily dose of 100 mg for 4 weeks, followed by a drug-free period of 2 weeks. The adverse reactions were mild, and she underwent the 2nd and further courses of therapy on an outpatient basis. Since she had acute cholecystitis during the 12th course, the drug was withdrawn for 2 months. Thereafter, the drug was started again after resolution of the cholecystitis. At present, ie, 3 years and 2 months after the surgery, the patient is receiving the 23rd course of chemotherapy on an outpatient basis, and abdominal CT shows no evidence of increase in the peritoneal metastases, enlargement of the intraperitoneal lymph nodes, or ascites.