A secondary aortoenteric fistula (AEF) is a direct communication between the gastrointestinal tract and the aorta in a patient who has undergone major surgery on the aorta, often an aorta graft operation. We experienced a patient who had undergone graft interposition for abdominal aortic aneurysm and was admitted due to three episodes of hematemesis and following hamatochezia. Gastroscopy, colonoscopy, and radioactive iodine scan failed to identify the bleeding site in the patient. He was diagnosed with AEF by double balloon enteroscopy and recovered after surgical intervention.