We encountered an extremely rare case of a saccular aneurysm of the descending aorta developing to the right of the spinal column with a normal left-sided aortic arch. An 80-year-old man was admitted to our hospital because of a saccular aneurysm of the right-sided descending aorta that had increased in diameter. Resection of the aneurysm and prosthetic graft replacement of the right-sided descending thoracic aorta were successfully performed under deep hypothermia through a right thoracotomy.