Vascular calcification is a tightly-regulated pathological process that is triggered by multiple factors ranging from extracellular mineral imbalance to pro-inflammatory cytokines and orchestrated by the osteogenic phenotypic transition of vascular smooth muscle cells (VSMCs). VSMCs secrete matrix vesicles (MVs), loaded with the calcification inhibitor fetuin-A, into the extracellular matrix and these serve as a nidus for calcification. Here we studied the mechanisms of MV secretion by VSMCs. Fetuin-A is internalized by VSMCs and delivered to late endosomes/multivesicular bodies and secreted in MVs via the exosomal pathway. Biochemical analysis showed that MVs originate from multivesicular bodies and are enriched with exosomal markers including CD9, CD63 and Tsg101. Proteomic analysis showed that VSMC exosomes partially share proteomic composition with exosomes secreted by other cells and are enriched with proteins involved in the regulation of cell adhesion and migration. Furthermore, fetuin-A secretion and VSMC MV secretion were blocked by GW4869, an inhibitor of sphingomyelin phosphodiesterase 3 (SMPD3) which regulates exosome biogenesis. Treatment of VSMCs in the presence of elevated extracellular calcium resulted in a significant increase in exosome secretion and this was associated with the upregulation of SMPD3 expression. Inhibition of SMPD3 prevented VSMC calcification indicating that exosome secretion is required for the initiation of VSMC calcification. Next we examined how the phenotypic transition influences exosome secretion and VSMC calcification. Heparin and TGF-β treatment markedly reduced VSMC proliferation and induced expression of VSMC contractile markers, calponin and α-smooth muscle actin. In contrast, treatment with the pro-inflammatory cytokine TNF-α induced VSMC proliferation accompanied by a reduction in contractile phenotype markers. Comparing exosome secretion revealed a significant increase in exosome secretion in the presence of TNF-α and reduced exosome production by the heparin or TGF-β treated VSMCs. Finally, in agreement with our in vitro data, EM analysis of longitudinal sections of VSMCs in human vessel rings ex vivo revealed MVB-like structures in VSMCs. Immunohistochemical staining of normal and atherosclerotic human aortic and carotid artery samples showed no presence of exosomal marker CD63 in the normal vessel wall. However, extensive CD63 staining was observed in the atherosclerotic vasculature particularly in association with calcified VSMCs. In conclusion, we found that fetuin-A is recycled via exosomal pathway and VSMC exosome secretion is regulated by SMPD3. Modulation of exosome secretion by mineral imbalance and phenotypic transition as well as loading with fetuin-A are novel regulatory pathways for VSMC calcification.