Aneurysm of the ductus arteriosus is rare, especially in adults, and preoperative diagnosis is very difficult, requiring intraoperative diagnosis. A 71-year-old man was preoperatively diagnosed with ductus arteriosus aneurysm by computed tomographic scanning, magnetic resonance imaging, and aortography, which demonstrated a saccular aneurysm of the distal aortic arch. Under partial extracorporeal circulation, the aneurysm was replaced by an artificial vascular graft. The location and morphology of the aneurysm confirmed the preoperative diagnosis. The postoperative course was uneventful. Surgery for this condition is safe and is recommended the same as for common thoracic aortic aneurysm.