The incidence of heterotopic gastric mucosa located in the submucosa in resected stomach specimens has been reported to be 3.0 to 20.1%. Heterotopic gastric mucosa is thought to be a benign disease, which rarely becomes malignant. Heterotopic gastric mucosa exists in the gastric submucosa, and gastric cancer rarely occurs in heterotopic gastric mucosa. Since tumors are located in the normal submucosa, they appear as submucosal tumors during endoscopy, and are diagnosed through endoscopic biopsies with some difficulty. For such reasons, heterotopic gastric mucosa is mistaken as gastric submucosal tumor. Recently, two cases of early gastric cancer arising from heterotopic gastric mucosa in the gastric submucosa were treated. Both cases were diagnosed as submucosal tumors based on upper gastrointestinal endoscopy, endoscopic ultrasound, and computed tomography findings, and in both cases, laparoscopic wedge resections were performed, the surgical findings of which also suggested submucosal tumors. However, pathologic assessment of the surgical specimens led to the diagnosis of well-differentiated intramucosal adenocarcinoma arising from heterotopic gastric mucosa in the gastric submucosa.