Quadricuspid aortic valve is an uncommon congenital anomaly and cause of aortic regurgitation. We report two cases of quadricuspid aortic valve with aortic regurgitation. Case 1, a 51-year-old woman was admitted to our hospital for fatigue and chest tightness. She had to and fro murmur along the left sternal border. Transthoracic echocardiography and transeso- phageal echocardiography showed grade 2-3 aortic regurgitation with quadricuspid aortic valve. The aortic valve consisted of four cusps of equivalent size(Hurwitz type a). Case 2, a 35-year-old man was admitted to our hospital for exertional dyspnea and chest tightness. He had grade 4/6 to and fro murmur along the left sternal border. Transthoracic echocardiography showed grade 4 aortic regurgitation with suggested quadricuspid aortic valve. The aortic valve consisted of two equal larger cusps and two equal smaller cusps and a supernumerary cusp located between the right and noncoronary cusps(Hurwitz type c). He was performed aortic valve replacement with a 21 mm On-X valve.