Backgound : The pulmonary veins(PV) often provide triggers or drivers of atrial fibrillation(AF). It has been shown that left atrial circumferential ablation (LACA) is more effective than PV isolation in eliminating AF. A procedural success in patients who underwent LACA has been also known to be associated with left atrial (LA) size reduction. However, it is not clear whether the efficacy of LACA compared to PV isolation depends on LA volume. Method: One hundred-thirteen consecutive patients with symptomatic drug refractory paroxysmal, or persistent AF were included in the present study. All enrolled patients underwent either PV isolation or circumferential ablation. LA volume was measured by transthoracic echocardiography before the procedure. Results: The mean age was 52.7 짹 9.9 years (range 30 to 72). Paroxysmal AF was present in 81 (72%) and persistent AF in 31(28%) patients. There was recurrence in 43 (38%) patients after procedure. Recurrence in persistent AF group was more than in paroxysmal AF group ( 74.2 % vs. 30.8% , P<0.001). There was a trend of less recurrence in circumferential ablation group, but it was not statistically significant (P=0.052). In the large LA volume group, circumferential ablation group showed less recurrence than PV isolation group ( 30.8 % vs. 84.6 %, P=0.002). In the normal LA volume group, the type of ablation technique was not significantly associated with the outcomes (P>0.05). Multivariate Cox-regression analysis revealed that LACA in patients with large LA volume was significant independent predictor of the successful outcome( hazard ratio 5.86, 95% CI 1.69-20.28, p=0.005), whereas in all enrolled patients persistent AF was independent predictor of AF recurrence( hazard ratio 4.87, 95% CI 1.36-17.46, p=0.015). Conclusion: LACA was significant independent predictor of a successful outcome only in patients with large LA volume. This study suggest that the efficacy of LACA compared to PV isolation depends on LA volume, and a successful outcome in large LA may be attributable to modification of the arrhythmogenic substrate within the PVs