Aim To investigate the epigenetic regulation mechanism of oxidized lipoprotein(a)[ox-Lp(a)] injury on vascular endothelial cells. Methods Bioinformatics and luciferase reporter gene were used to screen candidate microRNA binding to 0,1- translocation enzyme 2 (TET2) mRNA 3’-UTR and verify their targeted binding tendency. 0 mg/L, 25 mg/L, 50 mg/L and 100 mg/L of ox-Lp(a) were incubated with HUVEC-12 vascular endothelial cell line for 24 h, or incubated with HUVEC-12 vascular endothelial cell line with 100 mg/L ox-Lp(a) for 0 h, 6 h, 12 h, 24 h, 48 h respectively. qRT-PCR and Western blot were used to detect TET2 mRNA and protein expression levels. The expression of hsa-miR-125a-5p was detected by qRT-PCR. The change of TET2 activity was analyzed by detecting 5hmc level. Transwell was used to detect the permeability of monoclonal vascular endothelial cells. Results Bioinformatic analysis and luciferase reporter assay showed that TET2 was the target gene of hsa-miR-125a-5p, and the binding energy of hsa-miR-125a-5p to the 3’-UTR of TET2 mRNA was low (－30.1 kcal/mol). The activity of TET2 protein and mRNA was inhibited by ox-Lp(a) in the dose and time-dependent manner. The best reaction dose and time of ox-Lp(a) was 100 mg/L and 24 h. The activity of TET2 was down-regulated by 100 mg/L ox-Lp(a), while the expression of hsa-miR-125a-5p was significantly up-regulated, and anti-hsa-miR-125a-5p could reverse it. Ox-Lp(a) significantly increased the permeability of monolayer endothelial cells, but could be partially reversed by anti-hsa-miR-125a-5p. Conclusion Ox-Lp(a) inhibited the expression and activity of TET2 and increased the permeability of monolayer vascular endothelial cells by up-regulating hsa-miR-125a-5p expression which targeted binding to 3’-UTR of TET2 mRNA.