We report the case of a noncuratively resected gastric cancer patient who was successfully treated with S-1 monotherapy, resulting in long-term survival of 96 months. A 72-year-old woman underwent noncurative resection of subtotal gastrectomy for advanced gastric cancer with conglomerated lymph node metastasis and pancreatic invasion. She received chemotherapy with S-1 monotherapy postoperatively. S-1 (100 mg/day) was administered orally after breakfast and dinner for 28 days followed by a 14-day break for a total of 52 months. Regular checkups with esophagogastroduodenoscopy, abdominopelvic computed tomography, and fluorine-18-fluorodeoxyglucose positron emission tomography revealed no evidence of cancer 96 months after the operation. The patient was effectively treated with long-term administration of S-1 after noncurative gastrectomy for advanced gastric cancer.