A rupture of a dissecting aneurysm of the aorta is life threatening disease and calls for emergency surgical treatment. The author recently experienced one case of ruptured dissecting aneurysm of the descending thoracic aorta complicated with left hemothorax who was recovered after emergency operation of Aug. 11, 1976. The patient was a 43 years old farmer with known hypertension [260/120] for 20 years but without any venereal disease and had experienced sudden throbbing chest pain. Chest film and aortogram revealed this case ruptured aneurysm of descending thoracic aorta complicated with left hemothorax. In this case, large dissecting aneurysm extend from proximal part of left subclavian artery below diaphragm and involved with 3.0 and 4.0cm sized elliptical rupture in proximal part of descending thoracic aorta. And so, neither fenestration procedure nor replacement of dacron artificial vessel was suitable for this case. Finally, only the rupture site of aneurysm was treated by covering with fibrous pleura and teflon patch. The post-operative management of this case was planned to control hypertension with antihypertensive drugs. The follow-up was possible up to date about 2months. The patient has been doing well with ordinary activities except mild chest discomfort.[KTCS 1977;1:82-89]