A 59-year-old man visited our department because of cholecystectomy. Preoperative CT revealed a tumor shadow measuring 50 mm in front of the right iliopsoas muscle. MRI showed a low signal intensity on T1-weighted images and a slightly high signal intensity on the T2-weighted image. PET-CT showed accumulation of FDG(SUVmax 5.39)in the tumor but no other abnormal accumulations. We performed tumor resection for diagnostic purposes because malignancy could not be ruled out owing to the large size of the mass. Intraoperative findings showed a well-circumscribed margin of the tumor without invasion to other tissues. The retroperitoneum was incised circumferentially along the tumor under laparoscopic guidance, and the tumor was resected. Histopathological and immunostaining findings were consistent with leiomyosarcoma. In laparoscopic surgery, the surgical margin is observed in detail through the magnifying effect. Therefore, laparoscopic surgery can be a surgical option for tumors that may be completely excised based on preoperative findings.