A 64-year-old woman had gastric heterotopic of the duodenal bulb without any specific complaints. The lesion with irregular excrescence was diagnosed by means of target biopsies through endoscopy, and 3 years later, no noteworthy changes were observed in the endoscopic findings of the lesion, and it was also proved by an endoscopic Congo red test that the excrescence had a function of acid output. This is the second report of congenital heterotopic gastric mucosa of the duodenum which was confirmed not only by histological, but also functional examination.