Long QT syndrome is a cardiac disorder of repolarization which is characterized by elctrocardiographic abnormalities including prolonged QT interval, T-wave abnormalities and polymorphic ventricular tachycardia known as Torsades de Pointes. Its clinical manifestation are recurrent syncope, seizure, and sudden death. Recently,we experienced Torsades de Pointes(TdP) by head-up tilt test in 24 year-old female patient presenting recurrent syncope and long QT interval. Beta-blocker and left cervicothoracic sympathetic ganglionectomy were not effictive, then we tried mexiletine. After mexiletine medication, the QT interval was significantly shortened and there was no more syncope.