We experienced a case of acute aortic dissection without an intimal tear. A 55-year-old woman with SLE presented with acute chest pain. TEE study showed dissection of the ascending aorta, and accompanied by pericardial effusion. An emergency operation was performed four hours after onset. Intraoperatively, thrombus was encountered in the false lumen of the ascending aorta and the proximal arch. However, intimal tear was not found. She underwent graft replacement of the ascending aorta and the total aortic arch, and had an uneventful postoperative course. Histological examination of a segment of ascending aorta showed no evidence of mucinous degeneration and pathological rupture of the elastic fiber.