BACKGROUND: Impaired angiogenic abilities of the microvascular endothelial cell (MVEC) play a crucial role in diabetes mellitus– impaired ischemic tissue repair. However, the underlying mechanisms of diabetes mellitus–impaired MVEC function remain unclear. We studied the role of serum-derived small extracellular vesicles (ssEVs) in diabetes mellitus–impaired MVEC function. METHODS AND RESULTS: ssEVs were isolated from 8-week-old male db/db and db/+ mice by ultracentrifugation and size/ number were determined by the Nano-sight tracking system. Diabetic ssEVs significantly impaired tube formation and migration abilities of human MVECs. Furthermore, local transplantation of diabetic ssEVs strikingly reduced blood perfusion and capillary/arteriole density in ischemic hind limb of wildtype C57BL/6J mice. Diabetic ssEVs decreased secretion/expression of several pro-angiogenic factors in human MVECs. Mechanistically, expression of enhancer of zest homolog 2 (EZH2), the major methyltransferase responsible for catalyzing H3K27me3 (a transcription repressive maker), and H3K27me3 was increased in MVECs from db/db mice. Diabetic ssEVs increased EZH2 and H3K27me3 expression/activity in human MVECs. Expression of EZH2 mRNA was increased in diabetic ssEVs. EZH2-specific inhibitor significantly reversed diabetic ssEVs-enhanced expression of EZH2 and H3K27me3, impaired expression of angiogenic factors, and improved blood perfusion and vessel density in ischemic hind limb of C57BL/6J mice. Finally, EZH2 inactivation repressed diabetic ssEVs-induced H3K27me3 expression at promoter of pro-angiogenic genes. CONCLUSIONS: Diabetic ssEVs impair the angiogenic property of MVECs via, at least partially, transferring EZH2 mRNA to MVECs, thus inducing the epigenetic mechanism involving EZH2-enhanced expression of H3K27me3 and consequent silenc-ing of pro-angiogenic genes. Our findings unravel the cellular mechanism and expand the scope of bloodborne substances that impair MVEC function in diabetes mellitus.