Aortic dissection is a challenging disease and the causes of that are well-known. Blunt chest trauma is one of the causes of aortic dissection. In such cases, nearly all cases involves the isthmic portion of descending aorta, but ascending aorta is involved in about 10. We experienced a patient who had ascending aortic dissection due to automobile accident and who showed spontaneous rupture of the aorta during operation. In this case, after installation of aortic line via left femoral artery, ascending aorta ruptured and a large amount of blood gushed out, which was suckered by cardiotomy sucker. A little delay of cardiopulmonary bypass may cause the fatal outcome in such a case because the bleeding from aorta is too much to be controlled. Fortunately, we controlled the bleeding with cardiopulmonary bypass and got the good outcome of this patient by interpositioning the vascular graft. One should suspect the possibility of aortic dissection in blunt chest trauma, and prepare all the facilities against bleeding due to rupture.