A successful operation on a 49-year-old female with aortitis syndrome associated with prosthetic aortic valve detachment was reported. Aortic valve replacement using SJM 25A had been performed for aortic regurgitation caused by aortitis. Though her C-reactive protein (CRP) was kept between (+/-) and (2+) with prednisolone administered, general fatigue suddenly appeared 4 years after the first operation. The blood sedimentation rate was 65 mm/30 min and CRP was (4+), and the echocardiography showed abnormal movement of the prosthetic valve with perivalvular leakage on admission. Aortography showed the valve detachment and abnormal movement due to enlargement of sinuses of Valsalva, one of which was transformed as a diverticulum and projected into Left ventricular cavity with moderate leakage. After the inflammation was well controlled, she was operated upon. Dilatation of sinuses, perforation of intima around the prosthetic valve were recognized as left ventricular-aortic discontinuity, but ascending aorta was not enlarged. So the prosthetic valve was suspended below coronary ostia with transmural mattress sutures from right atrium. Postoperative course was uneventful. The postoperative aortography revealed only trivial perivalvular leakage without abnormal movement of the valve. This was a rare case of the valve detachment in the aortitis patient.