Backgrounds: Mean platelet volume (MPV) is one of the platelet function indices which reflects the platelet production rate and stimulation. The elevated values of MPV are reported to be associated with cardiovascular diseases and cardiovascular risk factors, such as, impaired fasting glucose, diabetes mellitus, hypertension, hypercholesterolemia, obesity and metabolic syndrome. Coronary vasospasm is closely related to atherosclerotic coronary artery disease, since intravascular ultrasound studies reveal atherosclerotic plaques in almost any spastic segment. The relation between MPV and coronary vasospasm has not been studied before. The aim of this study is to evaluate the values of MPV in patients with coronary vasospasm. Methods: A total 696 patients (Age; 55.20 짹 12.26, Men; 46.4 %) with typical or atypical anginal symptoms underwent diagnostic coronary angiography (CAG) and Acetylcholine (Ach) provocation test. Among them, 183 patients were positive in Ach-provocation test. All subjects were divided into the Ach-induced vasospasm group (n=183) and control group (n=513). We evaluated the relation between MPV and Ach-induced vasospasm. Results: There was an inverse correlation between MPV and platelet count (r = -0.289, p <0.001). MPV was higher in Ach-induced vasospasm group compared with that in control group (respectively, 9.03짹1.37 fl vs. 8.69짹1.25 fl, p = 0.002) In multivariate analysis, MPV was a independent predictor for Ach-induced vasospasm (OR; 1.188, p=0.018). Conclusion: Our study shows that high MPV is an independent risk factor for coronary vasospasm.