We have experienced a case of hepatico-colonal fistula which is a rare complication after microwave coagulation therapy (MCT). A 78-year-old man was seen at the hospital because of melena. Rectal examination revealed a hard mass and pathological diagnosis was rectal cancer. Preoperative CT scan of the liver showed five metastatic lesions in segment 4, 5 and 6. Low anterior resection was performed combined with MCT irradiation to the liver metastasis under ultrasonography. The body temperature had remained consistently elevated above 38°C since postoperative day 3. A contrast enhanced CT scan showed several low-density areas with niveau formation, which were diagnosed as liver abscesses after MCT. Percutaneous transhepatic drainage to the each liver abscess was made and then the temperature dropped rapidly within normal range throughout the hospital stay. Three months after the operation, an asymptomatic hepatico-colonal fistula located between transverse colon and segment 6 was detected by colonoscopy and fistelography. Although postoperative course was uneventful except this fistulization, he died of recurrence in May 1999.