A 66-year-old male with a chief complaint of dysphagia was admitted to our hospital. Upper gastrointestinal endoscopy revealed a type 3 tumor on the gastric upper body, and pathological examinations of the biopsy specimens revealed a poorly differentiated adenocarcinoma. Computed tomography (CT) of the abdomen showed significant wall thickness of the stomach, and regional and para-aortic lymph node metastases. The CA19-9 level was high: 978 U/mL on admission. He received neoadjuvant chemotherapy using S-1 (120 mg/body, days 1-21) and cisplatin (108 mg/body, days 8) for faradvanced gastric cancer. After neoadjuvant chemotherapy, upper gastrointestinal endoscopy revealed that the gastric carcinoma had significant reductions in the size of its tumors, and CT showed that the lymph node metastases had disappeared, leading to a partial response. He underwent total gastrectomy, distal pancreatectomy, splenectomy and Roux-en Y reconstruction. Pathological examination of the resected specimens showed a small number of cancer cells in the submucosal layer, suggesting a Grade 2 pathological response, and gave a positive reaction to CA19-9 staining. The postoperative CA19-9 level decreased to a normal level. This case is diagnosed as CA19-9-producing gastric cancer. He was treated on an outpatient basis with adjuvant therapy.