Backgrounds: Platelets play a central role in the pathogenesis of coronary artery disease. Mean platelet volume (MPV) is an indicator of platelet activation, and has been demonstrated to be correlated with platelet reactivity. However, there was a debate in the relation between MPV and coronary artery disease (CAD). The aim of the current study was to investigate whether MPV is associated with CAD. Methods: We measured MPV in 760 patients (Age; 57.48 짹 12.98, Men; 42.8%) who were not taken any antiplatelet therapy. We divided patients into low MPV group (���7.80 fL, n=387)) and high MPV group (>7.80fL, n=373). We investigated the relation between MPV and CAD. We additionally measured platelet aggregation was evaluated by PFA-100 in 656 patients who were not taken any antiplatelet therapy and had not CAD. The relationship between MPV and platelet aggregation was evaluated by PFA-100. Results: Baseline clinical characteristics were similar between the two groups. There was an inverse correlation between MPV and platelet count (r = -0.261, p <0.001). MPV was not associated with CAD (p=0.403) but MPV was higher in acute coronary syndrome (ACS) compared with no CAD and stable angina group (Figure). No relationship was found between MPV and platelet aggregation (r = 0.007, p =0.867). Conclusion: This study showed that MPV is not related to CAD and platelet aggregation. Thus, MPV cannot be considered as a marker of platelet reactivity.