The patient was a 54-year-old male with proteinuria, which was first noted in 1984. Recently, the patient experienced aggravation of the proteinuria, which resulted in nephrotic syndrome. Renal biopsy revealed findings compatible with membranous nephropathy. While being treated with prednisolone (30 mg/day), the patient experienced intense abdominal pain of sudden onset, diarrhea, and melena. A tumor was demonstrated by abdominal ultrasonography and CT scan. A diagnosis of ischemic colitis was made by colonoscopy. FDP and fibrinogen levels were elevated, and abnormalities of the coagulation and fibrinolytic factors were found at the onset of the symptoms.