Development of an aneurysm in the thoracic aorta, intercostal arteries, or cerebral vessels is not an uncommon occurrence in patients with coarctation of the aorta. The mechanism whereby coarctation predisposes to aneurysm formation is incompletely understood and we suggest that in this case, an intrinsic factor in the wall of the aorta underlies the formation of aneurysms. Recently we experienced one case of COA associated with the thoracic aortic aneurysm and operation was done successfully. PDA was simply ligated and the aorta was cross-clamped proximally and distally and the area of constriction or aneurysmal site were excised. Postoperative course was uneventful and the patient was discharged 2 weeks after operation. Hypertension at upper extremities was controlled without any antihypertensive drugs after operation and the degree of regurgitation of mitral valve was improved postoperatively but long-term follow-up should be necessary.