Dissecting aneurysm has long been recognized as an ominous and highly lethal form of aortic disease. Aortic dissection are characterized by longitudinal separation of aortic media and extension proximally, distally or both from the site of intimal tear. DeBakey and associates defined three types based on where the process originates and how far extends. In type I, intimal tear is located in the ascending aorta and extend beyond the descending aorta. We experienced a case of dissecting aneurysm, Type I of DeBakey`s classification which dissection extend to the left iliac artery. The patient was 61 years old woman and suffered from excruciating pain on admission. Excision of aneurysm and ascending aorta reconstruction using to Dacron Vascular Prosthesis were performed under extracorporeal circulation. The post-operative course was uneventful and follow up is continued.