We reported a patient with advanced gastric cancer successfully treated with S-1 chemotherapy for three weeks. The patient was a 67-year-old man who had gastric cancer clinically diagnosed as cT3N1H0P0M0, stage IIIA. His treatment was supposed to be daily oral administration of 120 mg S-1 for 28 days. At 21 days, this treatment was stopped due to severe appetite loss. The histological diagnosis of the resected stomach revealed complete disappearance of cancer cells in the stomach and the regional lymph nodes. Our report suggested that S-1 may have a potent therapeutic effect in neoadjuvant chemotherapy for advanced gastric cancer.