We experienced a case of traumatic aneurysm of descending thoracic aorta by an automobile accident. The patient was 23-year-old-male with a traumatic aortic aneurysm [6x12cm] on the descending thoracic aorta just distal to the origin of the left subclavian artery. Exposure was obtained through a left posterolateral thoracotomy incision in the fourth intercostal space and then partial femoro-femoral cardiopulmonary bypass was established.After aortic cross- clamping, the aneurysmal sac was opened and repaired with interposition of Dacron vascular graft and aortic cross-clamping period lasted for 100 minutes. Postoperative bleeding and vocal cord paralysis were complicated, but bleeding was controlled by reoperation and vocal cord paralysis was improved. Follow up was continued for 14months and postoperative course was uneventful.