A woman in her sixties was admitted to our hospital because of lower left abdominal pain. The patient had been treated with radiotherapy for uterine cervix carcinoma and had been receiving hemodialysis for diabetic nephropathy. Computed tomography showed free intraperitoneal air and thickening of the sigmoid colon wall. She was diagnosed as having peritonitis associated with colon perforation. During surgery, perforations were detected at the sigmoid colon. We performed Hartmann s operation. The resected specimen showed multiple ulcers with necrotic tissue. On day 8 after the first operation, Entamoeba histolytica was identified in the resected specimen, and metronidazole was administered. On day 10, she was in shock, and computed tomography showed re-perforation of the colon. A colectomy with stoma at the transverse colon and ileostomy were performed. Metronidazole was administered to the stoma immediately after the second operation. Her general condition improved, and she was discharged on foot. Early diagnosis followed by early amebicidal therapy is the key to successful treatment of this disease.