Tetralogy of Fallot associated with atrioventricular canal defect is rare congenital anomaly. Because of complexity of the surgical corrections of two associated anomalies, the mortality of surgery has been high. We have experienced a case of the tetralogy of Fallot with atrioventricular canal defect in a 9-year-old boy of Down`s syndrome, and the anomalies were totally corrected with good result. Single Dacron patch was placed to close the ventricular septal defect and the pericardial patch for atrial septal defect. The right ventricular outflow tract was widened by infundibulectomy and pulmonary valvulotomy followed by Goretex patch in right ventricular outflow tract.