A 75-year-old man, in whom upper gastrointestinal endoscopy revealed a submucosal tumor in the greater curvature of the gastric angle, was hospitalized for further investigations. Since the tumor was shown to be located in the submucosal layer by endoscopic ultrasonography, we performed endoscopic mucosal resection. Pathological studies of the resected specimen revealed a gastrointestinal stromal tumor of the stomach. It was also formed that the tumor was connected not to muscularis propria, but to the muscularis mucosae. There has been no previous report about a case of gastrointestinal stromal tumor of the stomach arising from the muscularis mucosae in Japan.