We report a case of severe aortic regurgitation due to deformation of the right coronary cusp which remained in a double-folded shape. A 76-year-old woman was admitted in August 2015 for the evaluation and treatment of dyspnea. She had no history of rheumatic fever, syphilis, endocarditis, or chest trauma. During physical examination, a grade IV/VI diastolic murmur was noted along the left sternal border. Her chest x-ray film showed marked cardiomegaly with interlobular pleural effusion (Vanishing tumor). An aortography revealed abnormally dilated proximal part of right coronary artery as well as severe aortic regurgitation. At operation, the ascending aorta was exposed through median sternotomy with the patient on total cardiopulmonary bypass. The left and non-coronary cusps were easily identified and noted to be normal. The right coronary cusp was recognized to be turned inside out and stayed in a double-folded shape, which made mal-coaptation of cusps and caused aortic regurgitation. The size of the right coronary cusp was larger than other two cusps. A very large right coronary ostium which occupied almost all of the sinus of Valsalva was confirmed. The aortic valve was excised and reconstructed with glutaraldehyde-treated autologous pericardium. She had an uneventful recovery and was discharged on POD 32. The mechanism of how right coronary cusp became disfigured was discussed. We think that the lesions of the sinus of Valsalva and proximal part of the RCA may have caused the double-folded right coronary cusp abnormality.