We report herein a rare case of leiomyosarcoma arising from the greater omentum with concomitant liver metastases. A 63-year-old Japanese woman was admitted to our hospital with an elastic-hard mass in the abdomen, but no other symptoms. The findings of several examinations led us to suspect an omental leiomyosarcoma. A laparotomy revealed an elastic hard and foliaceous mass (12.5 x 9.0 x 8.0 cm) arising from the omentum, and six masses in the liver. The omental tumor was extirpated and chemotherapy was administered under the guidance of angiography. The final diagnosis was leiomyosarcoma of the omentum. About 9 months after the operation, multiple liver metastases were found and repeated chemotherapy was given, but without effect. A partial hepatectomy was done, accompanied by microwave coagulation therapy (MCT). She is currently well and asymptomatic, with no signs of recurrence, 1 year after the partial hepatectomy. Thus, surgical resection and MCT were effective against liver metastases of a leiomyosarcoma in this patient.