A 28 y/o female patient had noticed a pelvic mass and low abdominal pain was explored at a local hospital. A hypervascular tumor was noted in the mesentery of the sigmoid colon. At our hospital, sigmoid colectomy with colorectal anastomosis was performed. The patient had uneventful postoperative course and was discharged 10 days after surgery. Pathological report showed it was a hyaline vascular type of Castleman's disease. Serological test of HIV was negative. The patient did not receive chemotherapy or radiotherapy. She was last seen one month ago, two and half years following surgery, with good health. Castleman's disease is a rare disease and is well established as a distinct clinicopathologic entity. The lesion is rarely found in the sigmoid colon. Treatment should be tailored according to the histological variants and clinical types.