Accumulating evidence has suggested that homocysteine (Hcy) is an independent risk factor for atherosclerosis (AS). Hcy can promote vascular smooth muscle cell (VSMC) proliferation, which is pivotal in the pathogenesis and progression of AS. The aim of the present study was to investigate the epigenetic regulatory mechanism of microRNA (miR)‑143‑mediated VSMCs proliferation induced by Hcy. The results of a 3‑(4,5‑dimethylthiazol‑2‑yl)‑2,5‑diphe‑nyltetrazolium bromide assay revealed that VSMC proliferation was increased by 1.39‑fold following treatment with 100 mM Hcy, compared with the control group. The levels of miR‑143 were markedly downregulated in the Hcy group, compared with the control group, as determined using reverse transcription‑quantitative polymerase chain reaction analysis. In addition, the level of miR‑143 methylation was increased markedly in the VSMCs treated with Hcy, compared with the control, and was reduced following transfection with DNA methyltransferase (DNMT)3a small interfering RNA, determined using methylation‑specific‑PCR. The activities of DNMT3a luciferase were also altered accordingly in VSMCs transfected with pre‑miR‑143 and miR‑143 inhibitor, respectively. In addition, the expression of miR‑143 was observed to be inversely correlated with the mRNA and protein expression of DNMT3 in the VSMCs. Taken together, these findings suggest that DNMT3a is a direct target of miR‑143, and that the upregulation of DNMT3 is responsible for the hypermethylation of miR‑143 in Hcy-induced VSMC proliferation.