Supramitral ring is a very rare cardiac lesion which frequently associated other congenital anomalies of the heart and great vessels. We present a case of isolated supramitral stenosis ring of the left atrium without an associated lesion who have had operated in this hospital. He was 22 months old male and postoperative course was excellent. The importance of careful clinical examination, angiocardiography, echocardiography before operation is emphasized. Since this lesion is potentially curable by operation, repair with use of cardiopulmonary bypass should be performed without delay once the diagnosis has been made.