Objective To compare the sedative effect and safety of remimazolam and midazolam in synchronous electrical cardioversion in patients with atrial fibrillation.Methods Thirty-two patients with at-rial fibrillation receiving synchronous electrical cardioversion from January 2021 to December 2022 were en-rolled,22 males and 10 females,aged 18-80 years,BMI 20-30 kg/m2,ASA physical status Ⅱ or Ⅲ.The patients were randomly divided into two groups using random number table method:remimazolam group and midazolam group,16 patients in each group.The remimazolam group was sedated with 0.2 mg/kg of intra-venous remimazolam,and the midazolam group was sedated with 0.025 mg/kg of midazolam intravenously,and the drug injection time in both groups was 1 min.The anesthesia onset time,awakening time,and ori-entation recovery time were recorded.SBP,DBP,and SpO2 were recorded before anesthesia induction(T,),when the eyelash reflex was absent(T2),after the completion of electrical cardioversion(T3),and at the time of awakening(T4).Neurobehavioral cognitive state examination(NCSE)was performed 5 mi-nutes after the patients were awake,including language ability,structural ability,memory,calculation abil-ity and reasoning ability,and the pass rate of each ability test was calculated.The occurrence of adverse re-actions during surgery(body movement,apnea)and within 12 hours after surgery(nausea,vomiting,and chest pain)was recorded.Results Compared with the midazolam group,the anesthesia onset time,awak-ening time,and orientation recovery time in the remimazolam group were significantly shortened(P＜0.05).There was no significant difference in SBP,DBP,and Sp02 between the two groups at different time points.Compared with the midazolam group,the pass rate of the reasoning ability test was higher in the remimazolam group 5 minutes after awakening(P＜0.05).There was no significant difference in the inci-dence of adverse reactions between the two groups.Conclusion Compared with midazolam,remimazolam has faster onset of sedation,faster awakening,faster recovery of orientation in synchronous electrical cardio-version of atrial fibrillation,and faster recovery of reasoning ability in NCSE after synchronous electrical car-dioversion.