Congenital atrial appendage aneurysm is postulated to arise from a developmental weakness in the atrial wall in utero. It was first reported by Semans and Taussing in 1939. This anomaly is a very rare and can be confirmed by echocardiography, magnetic resonance imaging, computed tomography and operative finding. Clinically, patients are often asymptomatic and diagnosed incidentally ,but supraventricular arrythmias and systemic thromboembolism have been reported in some cases. Aneurysmectomy is recommended to abolish the arrythmogenic focus as well as eliminate a potential source of sytemic emboli. A 33-year-old man presented mild dyspnea and intemittent syncope was suspected of having a left atrial aneurysm and confirmed by echocardiography, computed tomography and cardiac catheterization. He underwent aneurysmectomy and had an uneventful postoperative course.