A 70-year-old woman was admitted to our department with epigastric discomfort and nausea over the duration of 1 month. An esophagogastroduodenoscopy showed the presence of a 1.0×1.0 cm-sized flat lesion with central ulceration at the greater curvature side of the antrum. A biopsy demonstrated the presence of an adenocarcinoma of well differentiated, intestinal type in the stomach. Endoscopic submucosal dissection was done and the diagnosis of a composite neuroendocrine carcinoma with an adenocarcinoma of the stomach was confirmed. We report a case of a gastric composite tumor with an adenocarcinoma and neuroendocrine carcinoma confirmed by endoscopic submucosal dissection with a review of the literature.