Primary aortoduodenal fistula (ADF) is a direct communication between the abdominal aorta and the gastrointestinal tract without any previous vascular intervention and represents a rare but critical cause of repeated and massive gastrointestinal bleeding. Primary ADF often occurs as a result of atherosclerotic aneurysm and infection, but ADF involving a normal-size aorta is rare; furthermore, ADF related to radiation therapy is extremely rare. We present the case of a 56-year-old man with a history of bowel obstruction due to radiation enteritis who was admitted with severe hematemesis and hemorrhagic shock. Gastroduodenal endoscopy and contrast-enhanced computed tomography findings were unremarkable. Aortoduodenal fistula was suspected based on the diffuse calcification of the abdominal aorta confined to the radiation field and the presence of an aortoduodenal communication on angiography. Endovascular repair with a stent graft seemed to be a safer option than open surgery and was suited to the rapid control of bleeding from ADF because of the patients' unstable hemodynamic state and the presence of intestinal adhesions. The fistula was successfully sealed by endovascular stent graft placement. Hematemesis did not recur postoperatively and anemia gradually improved. The patient died from pneumonia 33 days later.