Objective To analyze the characteristics of surface electrocardiographic (ECG) and intracardiac electrophysiological mapping of atrial premature contractions (APC) and atrial fibrillation (AF) originated from the superior vena cava (SVC), so as to investigate the electrophysiological mechanism of AF with SVC origin. Methods The clinical data of 12 patients(mean age 55.3±12.2 years) with paroxysmal AF were retrospectively analyzed; the patients were electrophysiologically confirmed with AF of SVC origin and were hospitalized for radiofrequency ablation during Sept. 2006 to Aug. 2010. The P waves of APC from SVC in inferior leads and V1, morphology of AF, procedure time, ablation sites within SVC, complications and success rate were all analyzed. Results Compared with P wave of sinus rhythm (SR), the P amplitude of APC from SVC was significantly greater ( mV vs mV, P<0.05) in lead Ⅱ, and in lead V1 the ratio of biphasic morphology was significantly higher (91.6% vs 33.3%, P<0.05). The figures of fibrillation wave were similar to P waves of SR and APC in 8 patients (8/12,66.6%). Compared with the electrical isolation of left superior pulmonary vein (LSPV), SVC isolation needed a significantly shorter time ( min vs min, P<0.05)and a significantly less ablation site ( vs , P<0.05). Eight patients still presented persistent rapid firing within SVC after isolation; two patients suffered paroxysmal atrial flutter 1 month after procedure and were controlled by antiarrhythmia drugs. No patients had complications. Conclusion The APC and AF of SVC origin manifest specific ECG patterns, which helps to predict the target vena before ablation; the isolation of SVC needs a shorter time period and less ablation points, and with high success rate.