We report a patient with unresectable advanced gastric cancer who was successfully treated with chemotherapy after gastrojejunostomy. A 64-year-old man was admitted to our hospital complaining of appetite loss and body weight loss. Abdominal enhanced CT revealed a gastric wall thickening and swelling of lymph nodes in the lesser curvature. Upper gastrointestinal endoscopy showed a gastric cancer in the antrum of the stomach. He underwent laparotomy, which revealed a T4 tumor invading the pancreas. Gastrojejunostomy was performed. After the operation, intake therapy of 80-100 mg S-1 was started for four weeks followed by two weeks rest as one course. After 2 courses of the therapy, abdominal enhanced CT showed a partial response of the lymph nodes. He is alive for 19 months after the operation. Abdominal enhanced CT showed a stable disease. This case suggested that S-1 chemotherapy after gastrojejunostomy was effective for unresectable advanced gastric cancer because of the long-term survival and an improvement of the patient's quality of life.