Platelet size, measured as mean platelet volume (MPV), is associated with platelet reactivity. MPV has been identified as an independent risk factor for future stroke and myocardial infarction. The aim of the study was to determine the impact of MPV on the development of stoke in atrial fibrillation patients. We analyzed MPV, N-terminal pro B-type natriuretic peptide (NT-proBNP), red cell distribution width (RDW) in 200 atrial fibrillation patients (mean age, 69 years; 56% male). The primary endpoint was stroke free survival. The mean MPV was 8.46짹1.01 fL and median NT-proBNP was 1917 (IQR 810-4427) pg/mL. The mean RDW was 13.96짹1.27 %. There were 14 incident stroke events during a mean of 15.1 months of follow up. The Kaplan-Meier analysis revealed that higher tertile MPV group (���8.9 fL) had a significantly higher stroke rate compared with lower tertile MPV group (<8.0 fL) (14.7% vs 3.1%, log-rank: p = 0.01). A higher MPV was an independent predictor of stroke risk after adjusting age, sex, warfarin medication, NT-proBNP and RDW level (hazard ratio: 4.921, 95% CI 1.042-23.232, p = 0.044) in Cox proportional hazard analysis. We demonstrated that MPV was a predictive marker for stroke and its predictive power for stroke was independent of NT-proBNP and RDW level in patients with atrial fibrillation.