Microparticles are membrane vesicles with procoagulant and proinflammatory properties released during cell activation. Elevated levels of microparticles have been reported in many cardiovascular diseases. Here, we have characterized the cellular origins and studied the effects on endothelial cells of circulating microparticles from healthy subjects and patients with metabolic syndrome (MS), which is referring to the clustering of several cardiometabolic risk factors, including abdominal obesity, hyperglycaemia, dyslipidaemia and elevated blood pressure. MPs were obtained from whole blood of healthy and MS subjects by serial centrifugations. Then, their counts and cellular origins were determined by flow cytometry in platelet-free plasma. Human endothelial cell line Eahy 926 was treated for 24h with circulating concentration of MPs and subjected to measurement of both nitric oxide (NO) and superoxide anion (O2-) by electronic paramagnetic resonance. Enzymes linked to NO pathway were also analyzed by Western Blotting. Patients with MS displayed increased circulating levels of microparticles compared to healthy subjects (14718.4±4095.5 vs. 5770.2±2029.9 events/µL of plasma). Levels of platelets-derived (CD41+), endothelial-derived (CD144+ and CD146+), erythrocytes-derived (CD235+) and procoagulant (Annexin V+)microparticles were also increased in MS patients versus healthy subjects. However, microparticles derived from granulocytes (CD66b+)and leukocytes (CD45+) were not significantly different between MS and healthy subjects. In vitro treatment of Eahy 926 cells with microparticles from MS patients but not from healthy subjects reduced both NO and O2- productions by 51% and 42%, respectively. Microparticles from healthy subjects did not affect neither endothelial NO-synthase (eNOS) expression nor enhanced its phosphorylation at both activator and inhibitor sites (Ser 1177 and Thr495, respectively) and did not modify caveolin-1 expression. Microparticles from MS also did not change eNOS expression or its phosphorylation at the activator site S1177 but they markedly enhanced its phosphorylation at the inhibitor site Thr495. Finally, MS microparticles did not modify caveolin expression. In conclusion, we demonstrate that patients with MS displayed increased circulating microparticles especially those originated from platelet, endothelial cells and erythrocytes as well as procoagulant microparticles. Interestingly, microparticles from MS reduce NO bioavailability rather by a mechanism independent to an increase of oxidative stress in endothelial cells via reduction of eNOS activity that probably accounts for endothelial dysfunction. Taken together these results highlight a relationship between increased circulating of procoagulant and platelet microparticles with endothelial dysfunction in MS.