We report a case of rare anomaly of quadricuspid aortic valve associated aortic regurgitation and severe mitral regurgitation due to infective endocarditis. A 50-year-old man was admitted to our hospital for fever and dyspnea. The transesophageal echocardiography showed severe aortic regurgitation due to four equal aortic cusps and severe mitral regurgitation due to infective endocarditis. At the operation, aortic valve and mitral valve were replaced with 23 mm and 29 mm SJM valves. His postoperative course was uneventful.