Marfan syndrome is an inheritable connective tissue with protean clinical manifestations involving the ocular, skeletal and cardiovascular system. It is well estabalished that a clinical hall marker and the major cause of morbidity in Marfan syndrome is aortic root dilatation and associated aortic dissection which begins just above the coronary ostia in ascending aorta. We report a rare case of Marfan syndrome with aortic dissection which began just below left subclavian artery in descending aorta. A 20-years old woman was admitted to Soonchunhyang hospital because of sudden onset of back pain. On phsical examination, she had characteristic Marfanoid feature. Chest X-ray and Echocardiography showed cardiomegaly and severe dilatation of ascending aorta. Chest CT and aortography showed severe aneurysm of ascending aorta and aortic dissection of descending aorta with intimal flap. she was treated with medical treatment because of poor general condition.