Background: The optimal antithrombotic strategy for patients with atrial fibrillation (AF) undergoing drug-eluting stent (DES) implantation is unknown. Methods and Results: The 622 consecutive AF patients undergoing DES implantation were prospectively enrolled. Among them, 142 patients (TT group) continued triple antithrombotic therapy comprising aspirin, clopidogrel and warfarin after discharge; 355 patients (DT group) had dual antiplatelet therapy; 125 patients (WS group) were discharged with warfarin and a single antiplatelet agent. Target INR was set as 1.8-2.5 and was regularly monitored after discharge. The TT group had a significant reduction in stroke and major adverse cardiac and cerebral events (MACCE) (8.8% vs 20.1% vs 14.9%, P=0.010) as compared with either the DT or WS group. In the Cox regression analysis, administration with warfarin (hazard ratio (HR) 0.49; 95% confidence interval (CI) 0.31-0.77; P=0.002) and baseline CHADS₂ score ≥2 (HR 2.09; 95%CI 1.27-3.45; P=0.004) were independent predictors of MACCE. Importantly, the incidence of major bleeding was comparable among 3 groups (2.9% vs 1.8% vs 2.5%, P=0.725), although the overall bleeding rate was increased in the TT group. Kaplan-Meier analysis indicated that the TT group was associated with the best net clinical outcome. Conclusions: The cardiovascular benefits of triple antithrombotic therapy were confirmed by reducing the MACCE rate, and its major bleeding risk might be acceptable if the INR is closely monitored. (Circ J 2010; 74: 701-708)