A 58-year-old woman who noticed an abdominal tumor in October 2002 was seen at the hospital because she was diagnosed as having an intraabdominal tumor on CT at another hospital in December 2002. On physical examination a fist-sized, well movable, and elastic hard tumor was palpable in the lower abdomen. CT and magnetic resonance imaging scans showed a tumor with heterogeneous internal structure. From angiographic findings, a tumor of the small intestinal mesentery fed by the 4^th and 5^th jejunal branches from the superior mesenteric artery was suspected, and on February 10, 2003, the patient was operated on. Upon laparotomy, a 12-cm sized tumor with nodal protrusions was present in the small intestinal mesentery of the jejunum where was apart from the Treitz' ligament by 50cm. A partial excision of the small intestine was carried out. Histopathological study revealed dense fascicular growth of spindle-shaped atypical cells. On immunostaining examinations the tumor showed α SMA (+), desmin (+), CD34 (-), c-kit (-) and s100 (-). Accordingly the tumor was thought to be leiomyosarcoma arisen from the small intestinal mesentery. The patient's postoperative course was uneventful and she has been free from recurrence.