A 27-year-old man was admitted to a hospital with a complaint of epigastric discomfort. Upper gastrointestinal endoscopy and endoscopic ultrasonography revealed an elevated lesion on the posterior wall of the upper gastric body, and a diagnosis of ectopic gastric pancreas was made. Follow-up endoscopy performed 5 years later revealed an increase in the size of the mass to approximately 5cm in diameter. The location, shape, and clinical course of the mass aroused a suspicion of malignancy; therefore, partial gastrectomy was performed. Histopathologically, the resected mass was diagnosed as ectopic gastric pancreas with chronic inflammation, fibrosis, and bleeding around the acinar cells.