MicroRNAs (miRNAs), small noncoding RNAs, can control gene expression by binding to their target genes for degradation and/or translational repression. Epigenetic mechanisms are defined as heritable changes in gene expression that do not involve coding sequence modifications. Both mechanisms play an important role in maintaining physiological functions and are also related to disease development. However, few studies report that miRNA-mediated epigenetic regulations are involved in atherosclerosis. In the present study, oxidized low-density lipoprotein (oxLDL) significantly increased primary human aortic smooth muscle cell (HASMC) migration through MMP-2/MMP-9 up-regulation associated with decreased DNA methylation levels. Either mRNA or protein level of DNA methyltransferase 3b (DNMT3b) showed a dose-dependent down-regulation in oxLDL-mediated HASMCs. Knockdown DNMT3b expression enhanced oxLDL-induced DNA demethylation levels of MMP-2/MMP-9. The expression of miRNA-29b (miR-29b), directly targeting DNMT3b, was up-regulated by oxLDL treatment in a dose-dependent manner. OxLDL-mediated MMP-2/MMP-9 up-regulation, DNMT3b down-regulation, and DNA demethylation were all attenuated after knockdown miR-29b expression by antagomiR-29b. We find that oxLDL can up-regulate miR-29b expression, resulting in DNMT3b down-regulation in HASMCs and epigenetically regulated MMP-2/MMP-9 genes involved in cell migration. These results show that miRNA-mediated epigenetic regulation may be a novel mechanism in atherosclerosis.