An 87-year-old male patient was admitted to our hospital with a chief complaint of vomiting. Gastroscopy revealed Type 0-Ⅱc+Ⅱa tumor at the posterior wall in the middle third of the stomach. A biopsy indicated moderately differentiated adenocarcinoma. Abdominal CT revealed no lymph node or distant metastases. The clinical diagnosis was cT2(MP), N0, M0, cStage Ⅰ. Laparoscopic distal gastrectomy with D2 lymphadenectomy was performed. The pathological findings revealed moderately differentiated adenocarcinoma containing synaptophysin, chromogranin A, and CD56-positive tumor cells. He was then diagnosed with adenocarcinoma with neuroendocrine differentiation. The pathological diagnosis was pT2(MP), pN0, M0, pStage ⅠB. MRI revealed multiple liver metastases 5 months postoperatively. S-1 alone chemotherapy was started, and the patient showed partial response(PR)after 3 courses, according to the Response Evaluation Criteria in Solid Tumor (RECIST).