Abstract: Objective To explore the role of microRNA（miR）-126 in the injury of vascular endothelial cells induced by tumor necrosis factor-α（TNF-α） and its possible mechanism. Methods ECV304 cells were cultured in vitro and randomly divided into four groups: control group（did nothing）, TNF-α group（added 100 μg/L TNF-α）, miR-126 negative group（transfected lipofectamine 2000+100 μg/L TNF-α） and miR-126 simulant group（miR-126 simulant+100 μg/L TNF-α）. Each group contented 6 duplicate samples. The expression of miR-126 was detected by quantitative real-time polymerase chain reaction（qRT-PCR）; MTT method was used to detect cell proliferation; the levels of interleukin（IL）-6 and IL-1β were detected by enzyme linked immunosorbent assay（ELISA）; and apoptosis was detected by flow cytometry; the expressions of vascular endothelial cell adhesion molecule-1（VCAM-1）, intercellular adhesion molecule-1（ICAM-1） and high mobility group protein B1（HMGB1） were detected by Western blot; and the target relationship between miR-126 and HMGB1 was detected by bifluoromycin activity test. Results Compared with control group, the expression of miR-126 and cell proliferation rate decreased, while the levels of IL-6 and IL-1β, apoptosis and protein expressions of VCAM-1, ICAM-1 and HMGB1 increased（all P＜0.05） in TNF-α group and miR-126 negative group. Compared with TNF-α group and miR-126 negative group, expression of miR-126 and cell proliferation rate increased, while the levels of IL-6 and IL-1β, apoptosis rate and protein expressions of VCAM-1, ICAM-1 and HMGB1 decreased（all P＜0.05） in miR-126 group. Compared with miR-126 negative+HMGB1 3’untranslated region（UTR）-wild type（Wt） group, luciferase activity decreased in miR-126 mimics+HMGB1 3’UTR-Wt group（0.43±0.05 vs 1.06±0.15, P＜0.05）. Conclusions MiR-126 can improve ECV304 cell activity, alleviate TNF-α induced vascular endothelial cell injury, and reduce inflammatory response. Those effects may be achieved by targeting HMGB1.