A 14-year-old women who had a history of aortic root replacement at 7 years old admitted our hospital due to dilatation of aortic arch aneurysm. Loeys-Dietz syndrome was diagnosed when she was 10 years old. Computed tomography showed 70 mm proximal arch aneurysm. Operative findings revealed brachiocephalic artery and left common carotid artery branched from aneurysm. Partial arch replacement was performed and distal anastomosis was made between left common carotid artery and left subclavian artery. Close observation by CT regularly is necessary and undergo aortic repair not to miss the timing of surgery.