A 53-year-old man was admitted hospital because of frequent vomiting and poor digestion. Abdominal computed tomography showed a tumor, about 5 cm in diameter at the duodeno-jejunal junction. A barium contrast duodeno-small bowel series revealed stenosis in the therd portion, where push enteroscopy could not pass with normal mucosa. The preoperative diagnosis was submucosal or mesenteric tumor. Open surgery was performed. The tumor derived from the mesenterium and involved the anal side of the small intestine. The tumor was removed with partial excision of the upper jejunum. The diagnosis of mesenteric desmoid tumor was confirmed, histologically.