A case of membranous septal aneurysm with aortic regurgitation (AR) in a 13-year-old male was reported. As AR was progressed rapidly in this case, aneurysmorrhaphy of membranous septal aneurysm and aortic valve plication were performed. The postoperative coarse was uneventful. It was considered that the course of AR was prolapse of aortic valve related with membranous septal aneurysm.