Background: Renin-angiotensin-aldosterone system (RAS) may be activated during atrial fibrillation (AF). It is unclear whether RAS inhibition may facilitate cardioversion from AF and may prevent acute recurrence of AF (ARAF). We thus investigated the effect of pretreatment with RAS blockers on cardioversion success and ARAF in patients with AF scheduled for elective cardioversion. Methods: This observational study included 356 patients with AF undergoing elective pharmacological or electrical cardioversion. Of these patients, 135 were not included based on exclusion criteria and the remaining 221 patients were divided into RAS group (n = 116, 69 male) or non-RAS group (n = 105, 58 male) based on precardioversion use of any RAS blocker. Results: Hypertension, coronary heart disease and heart failure were more frequent in the RAS group. Cardioversion from AF was more successful in the RAS group than in the non-RAS group (% 92 vs. % 82, p = 0.026). The rate of ARAF was lower in RAS group compared with that in non-RAS group (17% vs. 31%, p = 0.026). In multivariate analysis, pretreatment with RAS blockers in addition to shock number and enlarged left atrium, independently predicted ARAF (OR: 0.33, 95% CI: 0.15-0.75, p = 0.008). Independent predictors of cardioversion success were shock number and left atrial dilatation, but not use of RAS blocker. Conclusion: Precardioversion use of RAS blockers may reduce ARAF following successful cardioversion of AF, but did not improve electrical cardioversion.