We report a patient with an advanced gastric cancer complicated by pyloric stenosis who was effectively treated by S-1 mono-therapy after gastrojejunostomy. A 62-year-old man consulted a general practitioner for abdominal pain and anorexia. Gastric roentgenography and upper gastrointestinal endoscopy showed gastric cancer(Borrmann Type 3) with pyloric stenosis. He was referred to our department. He underwent laparotomy, which revealed a T4 tumor invading the pancreas head, but neither liver nor peritoneal metastasis. A gastrojejunostomy was made. After the operation, chemotherapy of S-1(120 mg/day, day 1-21)+cisplatin(100 mg/day, day 8)was administered. After 2 courses, level of tumor marker decreased remarkably and abdominal enhanced computed tomography showed a significant size reduction of lymph nodes and that direct invasion to the pancreas was not clear any more. Second laparotomy was carried out and curative surgery was performed. After 4 courses of S-1(120 mg/day, day 1 approximately 28)mono-therapy as adjuvant chemotherapy, bone metastasis was confirmed by scintigram. Then methotrexate+5-FU, irinotecan+cisplatin and cisplatin+paclitaxel were chosen as second-, third-and fourth-line chemotherapy, which were not effective for long. He died 572 a days after the initial surgery. In the past, gastrojejunostomy was regarded as useful palliative treatment for those with gastric outlet stenosis to ameliorate the QOL. As S-1 is taking major role in the chemotherapy for advanced gastric cancer recently, usefulness of bypass surgery for such patients is highlighted even for longer survival time.