BACKGROUND: Atrial fibrillation is one of the most common cardiac arrhythmias which has been recieved relatively little attention until recently.Despite the variety of treatment modalities including drugs,surgery,catheter ablation and devices,the overall treatment of atrial fibrillation is not always satisfactory.Phalmacotherapy is still the most commonly used treatment through the unfavorable side effects of antiarrhythmic drugs are problematic.The purpose of this study is to compare the efficacy of class Ic antiarrhythmic drugs,propafenone versus flecainide. METHODS: We treated one hundred eighteen patients with atrial fibrillation by class Ic antiarrhythmic drugs,propafenone or flecainide with/without DC cardioversion to convert to and maintain the sinus rythm. We compared the clinical findings,drug efficacy,side sffects of drugs between two groups. RESULTS: 30 patients were treated by propafenne and 88 patients by flecainide.21 and 60 patients in each group were lone atrial fibrillation,14 and 49 patients were paroxysmal atrial fibrillation.Mean duration of drug administration were 360.9,339.4 days,respectively.The convesion rate to sinus rhythm by drugs was 25.0% in propafenone group and 30.7% in flecainide group(p=NS).The 300 days-manitenance rates of sinus rhythm after conversion by drugs or DC cardioversion were 63,3%,70.4%(p=NS)respectively. The side effects of drugs were dizziness,nausia and vomitting in both group and 1st degree AV block,transient sinus node dysfunction and decreased visual acuity in flecainde group.The drugs were discontinued in 11(37.7%) and 26(29.5%) patients in each group due to recurrence of atrial fibrillation or side effects of drugs. CONCLUSION: This study suggests that propafenone and flecainide are comparably effective in maintaining sinus rhythm in atrial fibrillation patients.Futher prospective and large study is required to confirm this findings.