A 77-year-old man presented with epigastralgia. Gastrointestinal endoscopic examination showed advanced gastric cancer, type 3, in the distal antrum. The patient refused surgery and preferred chemotherapy. The regimen consisted of 80 mg/body/day of S-1, continuously administered from day 1-14, followed by discontinuation for 2 weeks. After 2 courses, the patient experienced fatigue and recurrent vomiting. Laboratory studies revealed severe anemia; the hemoglobin level was 5.5 g/dL. An upper gastrointestinal endoscopy revealed pyloric stenosis and significant tumor reduction. Therefore, distal gastrectomy was performed. Histological examination did not reveal any viable cancer cells in the stomach and lymph nodes. Thus, a Grade 3 postchemotherapeutic effect was revealed.