Mitral valve leaflet aneurysm (MVA) is a rare and potentially devastating complication of infective endocarditis. Here, we report the case of a 49-year-old man with mitral endocarditis who had an anterior MVA without aortic morphologic change and only mild regurgitation. By real-time 3D transesophageal echocardiography (TOE), we found two perforations and a hard mass in the aneurysm accompanied with severe regurgitation. The patient underwent valve replacement surgery combined with anti-infection treatment and was successfully discharged. In addition to the case report and literature review related to MVA, we also summarize the application value of RT-3D TOE in these cases.