We report a case of nonocclusive mesenteric ischemia (NOMI), which developed after grafting for a descending thoracic aortic aneurysm in a hemodialysis patient. On postoperative day 5, acute increases in serum enzyme levels developed. Emergency angiography revealed severe vasoconstriction in the superior mesenteric artery (SMA) and other splanchnic arteries. Therefore an infusion of papaverine hydrochloride was started into the SMA. Although serum enzyme levels decreased, metabolic acidosis occurred the next day. An emergency laparotomy revealed segmental diffuse necrotic small intestine and colon. Despite a resection of the small intestine and sigmoid colon, the patient died of septic shock several days later. NOMI is uncommon, but it is a catastrophic event that can occur after cardiovascular surgery. If intestinal gangrene is suspected, prompt mesenteric angiography and vasodilator therapy followed by exploratory laparotomy should be performed without delay.