Tumors of smooth muscle origin are relatively uncommon in the rectum. Patients with leiomyosarcoma are very infrequently encountered. The patient was a 59-year-old Japanese male, who presented complaining of difficulty of defecation and melena. Rectal examination revealed an elastic hard and smooth-surfaced tumor of walnut size at 4 cm on the left antero-lateral wall. Needle biopsy was performed and the tumor was resected trans- sacrally. Histopathologically the tumor, was diagnosed to be leiomyosarcoma. Although the patient received no postoperative chemotherapy or irradiation, he is living without any symptoms or signs of recurrence 5 years and 6 months after the surgery.