"Idiopathic long QT syndrome" is characterized by prolongation of the QT interval due to unusual electrocardiographic repolarization abnormality and associated with variable clinical manifestations from no specific symptoms in lifetime to syncope or even sudden death. The prognosis of this syndrome is very grave and motality is approximately 50% within 10 years among untreated symptomatic patients after the initial syncope. But this sudden onset syncope may be misdiagnosed as epilepsy, being treated with antiepileptic drug for many years. However, this high mortality has been significantly reduced to less than 5% by the effective therapy. Therefore, it is crucial to make an early and accurate dianosis. We exprienced a case of 34 months old male who presented with recurrent syncopal attacks. He had no specific neurological abnomal finding except congenital deafness. He had normal EEG and brain MRI findings but ECG showed prolonged QT interval (QTc= 0.5), findings of which were compatible with long QT syndrome. He is currently being followed at OPD, but the pateint is still experiencing syncopal attack despite of treatment with beta-blocker, atenolol. Therefore, we are considering an insertion of pacemaker or performing thoracic sympathectomy.