The patient, a 43-year-old Japanese man suffering from duodenal ulcer and reflux esophagitis, was admitted to our hospital because of submucosal tumor in the antrum and obstructive stenosis of duodenum. Several imaging tests could not rule out the possibility of malignant disease. Therefore, the patient was surgically treated. Pathohistological examination of resected tissue demonstrated Heinrich type I heterotopic pancreas in the gastric lesion and submucosal abscess in the duodenal lesion with stenosis. In this case, it was considered that the heterotopic pancreas caused chronic inflammation to form the gastric tumor, and submucosal abscess leading to the severe duodenal stenosis.