Backgroud: Branch retinal vein occlusion (BRVO) is the second most common retinal vascular disease after diabetic retinopathy. To date, the studies were unable to elucidate the mechanism of the thrombosis leading to the entity; particularly the relation between thrombocyte aggregation and retinal vein occlusion is still unclear. Mean platelet volume (MPV) is a determinant of rate of platelet production and activation, both of which are indices of function of platelets. The relation between MPV and BRVO has not been studied before. The aim was to evaluate MPV in BRVO. Materials and Methods: Forty patients were included in the study. Forty six age and sex matched hypertensive volunteers were recruited as the control group. Results: MPV values were significantly higher in BRVO patients compared with the control subjects (8.01 +/- 0.79vs 7.52 +/- 0.32fL, respectively; P < 0.001). Conclusion: MPV is significantly higher in patients hypertensive BRVO patients and further investigations regarding its potentially use as a prognostic biomarker in patients with BRVO are needed.