The most common treatment for patients of peritoneal dissemination of gastric cancer is a systemic chemotherapy, but the prognosis of these patients is very poor. For these diseases, some have reported the usefulness of intraperitoneal chemotherapy with cisplatin (CDDP), because of the direct cytotoxicity. Here, we report an effective treatment by chemotherapy with S-1 plus CDDP, intraperitoneal administration for the patients of peritoneal dissemination of gastric cancer. The patient was a 41-year-old male with upper abdominal pain. Upper gastrointestinal endoscopy showed a large type 3 gastric cancer from the cardia to antrum. Intraoperative peritoneal lavage cytology and dissemination was positive, thus we performed the total gastrectomy and implanted the intraperitoneal (IP) port in the Douglas's pouch. S-1 was given orally twice daily for the first 3 weeks of a 5-week cycle. CDDP was given as an intraperitoneal infusion on day 8 of each cycle. After 10 courses, he was treated with S-1 alone because he had an allergic reaction of CDDP. In 35 courses, he had survived for 5 years as disease free. Intraperitoneal chemotherapy may be a promising treatment for the patients who have peritoneal dissemination from gastric cancer.