Background: The anatomical and functional characteristics of the left atrial appendage (LAA) and its importance in patients with atrial fibrillation (AF) has not been clearly demonstrated. The aim of this study was to investigate functional and morphological features of the LAA in patients with AF referred for catheter ablation. Methods: Total 72 patients with AF patients including 50 paroxysmal AF (PAF, 55.311.8 years old, M:F=40:10) and 22 persistent AF (PeAF, 55.17.8 years old, M:F=19:3) were studied. 3-D CT which acquired within 24 hours before catheter ablation was utilized to assess anatomical characteristics of the LAA. LA angiography obtained by power injection of the contrast agent into the LA through pigtail catheter (6 Fr) was used to evaluate the neck diameter and ejection fraction (EF) of the LAA. The EF of the LV was 51.711.2% in PeAF and 56.75.4% in PAF group (NS). Results: The LA and LAA volumes were 136.046.4 ml and 13.25.8 ml in PeAF, which were greater than those with PAF (88.742.1 ml and 10.84.4 ml, p=0.001 and p=0.151, respectively). The ratio of LAA/LA volume (0.100.03) in PeAF group was smaller than that of PAF group (0.130.06, p=0.013). The LAA neck diameter (25.55.4 mm) in PeAF group was larger than those with PAF (22.14.2 mm, p=0.010). The EF of the LAA in PAF group was 76.311.3% and could not be calculated in PeAF. LA volume (p=0.005) and LAA volume (p=0.018) were significant predictors for the recurrence of AF during 16.7 months of follow-up, but EF of the LAA, LAA/LA volume ratio and LAA neck diameter were not. Conclusion: The LAA volume and LAA neck diameter in PeAF group were greater than those of PAF group along with LA volume. Both LA and LAA volumes were significant predictors of recurrence of AF after catheter ablation. The LAA is an important cardiac structure vulnerable to chronic remodeling process in AF.