We replaced the aortic root in a 43-year-old woman with Takayasu's aortitis associated with prosthetic aortic valve detachment. The patient's aortic valve had been replaced when she was 31 years old with a mechanical prosthesis to treat aortic regurgitation. Though C-reactive protein was kept almost normal with prednisolone, complete atrioventricular block suddenly appeared 12 years after the first operation. After the implantation of an artificial pacemaker, we closely followed up aortic root status. Aortography and echocardiography showed that the valve moved up and down, probably due to enlargement of the sinuses of Valsalva, without perivalvular leakage. We removed the prosthetic aortic valve, which was partially detached from the aortic valve ring at the right- and non-coronary cusps and successfully replaced the aortic root with a mechanical prosthesis inserted into a 26 mm woven graft. Although the postoperative course was uneventful, we closely continue to observe the case and to administer of antiinflammatory medication.