Objective To study the biological mechanism of curcumin in controlling the expression of microRNA-21 (miR-21) and alleviating injury of vascular endothelial cells (VEC) induced by oxidized low density lipoprotein (ox-LDL). Methods VEC were divided into blank group, model group (treated with 100 μg/mL of ox-LDL) and curcumin group (treated with 100 μg/ml of ox-LDL+50 μg/ml of curcumin). The proliferation capacity of VEC was detected by using CCK-8 assay. The abilities of proliferation, migration and invasion of VEC were detected by using wound-healing test and Transwell assay. The mRNA and protein expressions of proliferating cell nuclear antigen (PCNA) and matrix metalloproteinase-9 (MMP-9) and miR-21 expression level were detected by using RT-qPCR and Western blotting assay in all groups. Results The survival rate decreased significantly in VEC treated with different concentrations of ox-LDL, and survival rate of VEC treated with 100 μg/mL of ox-LDL was (58.916±3.138) %, which was used for establishing the model of VEC injury. The VEC proliferation capacity (P<0.01), migration ability [(33.063±3.532) vs. (64.397±4.648), P<0.01] and invasion ability [(256.667±11.865) vs. (404.333±10.105)] were lower in model group than those in blank group (P<0.01). The VEC proliferation capacity (P<0.01), migration ability (61.773±2.451, P<0.01) and invasion ability [(393.000±11.547) were higher in curcumin group than those in model group (P<0.01). The mRNA and protein expressions of PCNA (P<0.01) and MMP-9 (P<0.01) were lower in model group than those in blank group. The mRNA and protein expressions of PCNA (P<0.01) and MMP-9 (P<0.01) were higher in curcumin group than those in model group. The relative expression of miR-21 was (8.020±0.483) in model group, which was higher than that in blank group (P<0.01). The relative expression of miR-21 was (2.241±0.205) in curcumin group, which was lower than that in model group (P<0.01). Conclusion Curcumin can enhance the abilities of proliferation, migration and invasion of injured VEC induced by ox-LDL, inhibit miR-21 expression and improve VEC function.