A 50-year-old female patient underwent distal gastrectomy and intraperitoneal CDDP administration for advanced gastric cancer accompanied by severe peritoneal dissemination. She valued her quality of life and chose an oral anticancer drug, S-1, as a postoperative chemotherapy agent. S-1 was administered at a dose of 100mg/body/day for 4 weeks, followed by a 2- week rest. There were no adverse events due to S-1 and no exacerbation of peritoneal dissemination in the 5 years following surgery. The S-1 administration schedule was then changed to alternate-day administration. Eight years after the surgery, the patient discontinued S-1 treatment and has since survived for 11 years with no obvious cancer recurrence.