Background: The reverse remodeling of left atrial size and improvement of atrial function after cardioversion of atrial fibrillation (AF) is well documented. However, the detailed evaluation of left atrium (LA) structure and function has not been performed according to the method to treat AF. The objective of this study was to assess whether the morphological and functional changes of LA and left ventricle after radiofrequency catheter ablation (ABL) differ from those after electrical cardioversion (ECV) for AF. Methods: The AF patients who had maintained sinus rhythm for 3 months after ABL (n=33) and ECV (n=30) were included prospectively. The cardiac structure and function were examined by echocardiography at baseline, 1 week, 1 month, and 3-month after procedures. LA function was assessed with Doppler parameters (E and A wave velocity and E/A ratio) and tissue Doppler parameters (E쨈 and A쨈 velocity). Results: The mean duration of AF was longer in the ABL group than in the ECV group (62.6짹47.0 vs. 21.1짹17.5 months, p=0.000). The patients with paroxysmal AF was 66.7% (n=22) in the ABL group, and 3.3% (n=1) in the ECV group. After procedures, the LA size and volume decreased with linear trend across time period in both groups (p<0.05 for all variables), and the onset of decrement of the LA size and volume was within 1 month. The A and A쨈 velocity increased in the ECV group (p=0.000 and 0.004, respectively). As the baseline LA size is larger in ECV group than in ABL group (46.1 mm vs. 41.0 mm, p=0.001), sub-analysis was done. In patients with LA size ranging from 40 mm to 49 mm, the LA size and volume decreased in both group (p<0.05 for all variables) and the A wave velocity increased over 3 months only in ECV group (p=0.000). Conclusion; This study demonstrates that reverse morphological remodeling of the LA occurs both after successful ABL and ECV. However, improvement of LA function defined as increase of A and A쨈 was observed in the ECV group but not in ABL group. The clinical implication of these findings is that longer period of anticoagulation therapy may be needed in AF patients after ABL.