The purpose of this study was to investigate the time-dependent effect of statin treatment and echocardiographic epicardial fat thickness (EFT) on the maintenance of sinus rhythm (SR) in atrial fibrillation (AF) patients after electrical cardioversion (EC). One hundred sixty-three AF patients without previous statin treatment who underwent EC were consecutively enrolled. The maintenance rate of SR after EC (1, 3, 6, and 12 months) as documented by electrocardiogram and EFT were compared between patients with statin treatment (statin group, n = 63) and those without (no statin group, n = 100). There was no significant difference in the maintenance rate of SR between the groups soon after EC (statin group; 85.7 % vs. no statin; 84.8%, p = 0.535), after 1 month (71.0 vs. 59.1%, p = 0.091), and after 3 months (63.2 vs. 50.0%, p = 0.086). However, the maintenance rate of SR was significantly higher in the statin group compared to no statin group (61.8 vs. 42.9%, p = 0.024) after 6 months, and this significant difference persisted up to 12 months of follow up (60.1 vs. 36.4%, p = 0.001). Patients with recurrence showed higher baseline EFT (7.4 ± 2.7 vs. 8.5 ± 3.0 mm, p = 0.014). Multivariate linear regression analysis indicated that EFT, left atrial diameter, high-density lipoprotein cholesterol, statin treatment, and dose were the significant contributors to the maintenance of SR for all periods after EC. Statin treatment and low EFT were associated with a higher maintenance rate of SR in AF patients after EC. Significant benefit of statin was realized 6 months after EC, and this benefit was shown to be maintained over time.