Introduction: Left atrial diameter (LAD) is well known as one of the predictors for recurrence following catheter ablation in patients with atrial fibrillation (AF). However, there is an AF patient population who has never experienced recurrence after the ablation even in patients with enlargement of LA dimension, and vice versa. We hypothesized that different alterations of volume between the LA body and LA appendage (LAA) regardless of LAD can predict clinical outcome following catheter ablation in patients with AF. Methods: Among 386 consecutive patients (mean 55.6짹10.7 years, 78.8% male, 37% non-paroxysmal AF) who underwent catheter ablation of AF using a stepwise approach including circumferential pulmonary vein isolation, 284 patients with LAD<45 mm (mean 38.2짹4.4 mm) and 102 with LAD���45 mm (mean 49.2짹4.7 mm) were assessed, respectively. LAD was measured by transthoracic echocardiography, and volumes of LA and LAA were calculated by multi-detector CT scan before the procedures. Results: During the mean 21.9짹15.9 months, the rate of freedom from recurrence of AF/atrial tachycardia was higher in patients with LAD<45 mm compared with those with LAD���45 mm (80.3% vs 61.8%, p<0.001 by Log Rank). In patients with LAD<45 mm, both LAD, LAA volume and total LA volume (LA volume plus LAA volume) were significantly greater in patients with recurrence compared with those without recurrence (LAD: 40.1짹3.9 vs 37.8짹4.4 mm, p<0.001; LAA volume: 12.8짹12.2 vs 9.3짹4.0 ml, p=0.042; total LA volume: 104.1짹32.3 vs 92.3짹26.7 ml, p=0.008), whereas there was no significant difference in LA volume (91.4짹28.3 vs 87.1짹26.3 ml, p=0.280). In patients with LAD���45 mm, LAA volume was significantly larger in patients with recurrence than in those without recurrence (15.5짹8.9 vs 11.8짹5.6 ml, p=0.024), however, there were no significant differences in LAD (49.9짹5.2 vs 48.8짹4.4 mm, p=0.257), LA volume (147.7짹44.9 vs 135.8짹45.7 ml, p=0.204) and total LA volume (161.3짹52.9 vs 143.0짹51.4 ml, p=0.126). Multivariate analysis showed that in patients with LAD���45, LAA volume independently associated with the recurrence after AF ablation (hazard ratio 1.048, 95% CI 1.009-1.089, p=0.016). Conclusions: LAA volume is an independent pre-procedural predictor of long-term success after catheter ablation of AF in patients with enlarged LA (LAD���45 mm). These findings suggest that the distinctive structural remodeling occurring in the LAA may be an important substrate of chronic AF related to recurrence of AF after catheter ablation.