An aortoesophageal fistula, an abnormal anatomical communication between the aorta and the esophagus, is a rare cause of upper gastrointestinal bleeding. The mortality rate of patients with this condition is very high. A 77-year-old man, who had undergone endovascular aortic repair for a ruptured abdominal aortic aneurysm, developed melena. An upper gastrointestinal endoscopy was performed. This detected an esophageal ulcer, which had the potential to develop into an aortoesophageal fistula. Therefore, thoracic endovascular aortic repair was performed on the following day. Thereafter, the course was uneventful. We encountered a rare case of an esophageal ulcer associated with a thoracoabdominal aortic aneurysm before it developed into an aortoesophageal fistula.