Aim To investigate the clinical significance of microRNA-126 （miR-126） expression level in peripheral plasma from type 1 diabetic patients and the relationship between miR-126 expression level and the endothelial injury of type 1 diabetes mellitus. Methods The miR-126 expression level was investigated in plasma from 47 type 1 diabetic patients and 50 healthy matched controls by real-time fluorescent quantitative polymerase chain reaction （PCR）. The expression of endothelial nitric oxide synthase （eNOS） was measured by enzyme-linked immunosorbent assay （ELISA）. The relationship between miR-126 and the endothelial injury of type 1 diabetes mellitus was analyzed by correlation analysis. Results The miR-126 expression level was significantly decreased in the group of T1DM compared to control group. Also, the expression of eNOS was significantly decreased in the group of T1DM. MiR-126 was positively correlated with eNOS. Conclusions The expression level of miR-126 in peripheral plasma from type 1 diabetic patients was lower than that of the healthy controls. T1DM patients were often accompanied with endothelial dysfunction and vascular complications, so this indicated that the decreased expression of miR-126 was involved in the endothelial dysfunction of T1DM. MiR-126 may be mediated by endothelial injury and participate in the development and progression of diabetic vascular complications.