Mesenchymal stem cells (MSC) are multipotent cells that possess regenerative functions that are of interest for in osteoarticular diseases such as osteoarthritis (OA). These functions are thought to be primarily mediated by mediators released within extracellular vesicles (EV). The aim of this study was to compare the immunomodulatory effects of two major types of EV, exosomes and microparticles, secreted by MSCs. EV subsets were isolated from murine primary MSCs by ultracentrifugation. Size and structure were evaluated by Dynamic Light Scattering and electron microscopy. Expression of membrane and endosomal markers was tested by flow cytometry. Proliferation of murine splenocytes was quantified after 72h of incubation with EVs after CFSE-labelling. Phenotypic analysis of T lymphocyte subpopulations was also performed by flow cytometry. In vivo, EVs were injected in the knee joint in the collagenase-induced osteoarthritis (CIOA) model and histological score was performed. In vitro functional analysis indicated that addition of microparticles or exosomes in proliferative assays inhibited the proliferation of total splenocytes in a dose-dependent manner. Analysis of T cell subpopulations revealed a decrease in CD8⁺IFNγ⁺ lymphocytes and an increase in both CD4⁺IL10⁺ Tr1 and CD4⁺CD25⁺FOXP3⁺ Treg cells. This immunomodulatory function of EVs was also observed in vivo in the CIOA model. In summary, our data indicated that the immunosuppressive effect of MSCs is in part mediated by exosomes and microparticles that play in vivo a major role in MSC-mediated therapeutic effect by reducing osteoarthritic symptoms.