Atrial fibrillation occurring in patients with Wolff-Parkinson-White(WPW) syndrome is a potentially life threatening arrhythmia because it lead to ventricular fibrillation which may be caused by a rapid ventricular response because of one or multiple accessory pathways with a very short anterograde refractory period. The incidence of sudden cardiac death by ventricular fibrillation in the WPW syndrome ranged from 0 to 0.6%. To avoid the sudden cardiac death, atrial fibrillation in the WPW syndrome should be terminated immediately by direct current cardioversion or intravenous administration of antiarrhythmic drug, especially sodium channel blocker. Radiofrequency catheter ablation on the accessory pathways is a first line treatment to prevent ventricular fibrillation.