Abstract Background There is no detailed guideline recommendation of AAD treatment for the firstly developed paroxysmal atrial fibrillation (AF). Anti-arrhythmic drugs (AAD) prevent recurrence of AF and short-term AAD treatment would increase drug safety by reducing treatment duration. Introduction We designed the prospective, randomized trial to evaluate the efficacy of short- and long-term AAD (flecainide) compared with no treatment in maintaining sinus rhythm in patients with firstly developed paroxysmal atrial fibrillation (PAF). Methods Definition of the firstly developed PAF was the patients with firstly developed symptomatic PAF without history of palpitation. Sixty patients were randomly assigned into no AAD treatment (Group I; N=21), short-term AAD treatment (flecainide 100mg bid for 4 weeks, Group II; N=20) or long-term AAD treatment (flecainide 100mg bid for 6 months, Group III; N=19). All patients were in sinus rhythm at randomization. Patients received clinical follow up with serial evaluation of rhythm status. Results There were no significant differences in age, gender, cardiovascular comorbidities and echocardiographic parameters. Among the total population, AF recurred in 16 patients (26.7%) during the follow up period. AF free survival was significantly different among groups (p=0.038) (Fig 1). Conclusions Long-term AAD at least 6 months is beneficial in maintaining sinus rhythm than no or shot-term AAD in patients with firstly developed PAF.