Fetal ductus arteriosus aneurysm is characterized by a localized saccular or tubular dilatation of the ductus arteriosus. It is likely to develop in the third trimester because of the abnormal cushion formation or elastine expression. The role and pathogenesis in fetal life are, however, unknown. Although fetal ductus arteriosus aneurysm usually resolves itself after birth following the closure of the ductus arteriosus, severe complications, such as spontaneous rupture of the aneurysm, thromboembolic formation, compression of the surrounding tissues, infection and even sudden death, have been described postnatally. It is rarely reported in Korea to date. We report a case of ductus arteriosus aneurysm prenatally diagnosed by fetal echocardiography at 37 weeks 1 day’s gestation