An 81-year-old man was admitted to a primary care hospital due to bloody diarrhea. The findings of abdominal computed tomography indicated ischemic colitis, so conservative therapy was started. On the 4th hospital day, the patient was transferred to our hospital because of renal dysfunction. Physical examination showed clouding of consciousness and abdominal distention. Abdominal computed tomography revealed massive ascites and thickening of the whole colonic wall. With a diagnosis of acute abdomen, an emergent laparotomy was performed. Extended right hemicolectomy was performed because of severe ischemic change and necrosis of the right side of the colon. In the stool culture before the operation, Escherichia coli O157 and verotoxin were found, so this case was diagnosed as hemorrhagic colitis with hemolytic uremic syndrome and acute encephalopathy due to Escherichia coli O157 infection. Postoperatively, the hemolytic uremic syndrome and acute encephalopathy were prolonged. However, with intensive care, the patient recovered and was discharged on the 33rd postoperative day.