Background: Electrical cardioversion for atrial fibrillation(AF) can restore sinus rhythm(SR) immediately with high success rate. But there were debates about predictors of long-term maintenance of SR. The aim of this study was to identify predictors for long-term SR maintenance after electrical cardioversion for AF. Methods: This retrospective study included 54 consecutive patients (41 males, age 57.8짹8.2 years) who underwent electrical cardioversion for AF. Immediate success rate and long-term maintenance rate of SR were evaluated. Classification and regression tree(CART) and multivariate analysis were used to identify the predictors for SR maintenance. Results: SR was restored immediately in 47 of 54 (87.0%) patients after electrical cardioversion. 22 of 47 (46.8%) patients were remained in SR during follow up (mean follow up duration 29.8짹21.6 months). CART analysis identified a duration of AF before cardioversion<204.5 days (AF duration<204.5) was the best predictor of SR maintenance. The next best predictor was body mass index(BMI)<25.9 kg/m짼. Multivariate analysis also identified AF duration<204.5 was a useful predictor for SR maintenance (odd ratio[OR] 4.38; 95% confidence interval[CI] 1.16-16.53; P=0.029). The patients with AF duration<204.5 and BMI<25.9 kg/m짼 showed higher possibility of SR maintenance (OR 19.40; 95% CI 2.15-174.87; P=0.008). Conclusion: After successful electrical cardioversion of AF, duration of AF and BMI of the patients were useful predictors for long-term maintenance of SR.