Objective To investigate the value of 12-lead Holter for the diagnosis of unexplained syncope so as to provide the evidence for clinical diagnosis and treatment.Method 127 cases of patients with unknown syncope were received 12-lead Holter monitoring and were asked to induce syncope as much as possible in the monitoring process and record syncope time and ECG changes.Results 34 cases of patients had the occurrence of syncope in the monitoring process

including 28 cases of arrhythmia

accounting for 82.3%.In the 28 cases of arrhythmia

the proportion of sinus bradycardia with sinus arrest was the highest（39.3%）

followed by atrioventricular conduction block

supraventricular arrhythmias and ventricular arrhythmia.The occurrence of syncope was related with ventricular asystole time and ventricular asystole time equal or longer than 3.0seconds increased the incidence of syncope.Conclusion The application of 12-lead Holter has a great significance on the diagnosis of cardiogenic syncope and can provide the reference for its diagnosis.