Gastric hyperplastic polyps are generally considered benign lesions, although rare cases of adenocarcinoma have been reported. Two cases of intramucosal adenocarcinoma originating from gastric hyperplastic polyps that were successfully removed by endoscopic mucosal resection or endoscopic submucosal dissection are reported. On pathological examination, adenocarcinoma limited to the hyperplastic foveolar epithelial mucosa of the gastric hyperplastic polyps was observed.