A 40-year-old man was referred to our hospital because of severe anemia and small intestinal tumor revealed by computed tomography. The enteroscopy exam showed the intraluminal penetration of the tumor, which was considered as a cause of anemia. Although emergency operation was performed laparoscopically, intraoperative findings indicated tumor invasion into peritoneum, and we converted from laparoscopic surgery to open surgery that included concomitant peritoneum resection. Histopathological findings showed spindle-shaped tumor cells with severe atypia. Immunohistochemical study showed tumor cells to be positive for aSMA, but negative for c-kit and CD34, then we diagnosed the tumor as leiomyosarcoma of the ileum. Since leiomyosarcoma of the small intestine is a rare entity, we have reported with literature consideration.