Objective To investigate the regulatory effect of miR-451a on macrophage migration inhibitory factor (MIF) and its effect on the proliferation of hepatocellular carcinoma HepG2 cells. Methods Real-time quantitative PCR was utilized to detect the expression of miR-451a and MIF mRNA in clinical liver cancer tissues. The luciferase reporter system was used to validate the regulatory relationship between miR-451a and MIF. The lentivirus overexpression vector of miR-451a was packaged to infect HepG2 cells. The expression of miR-451a and MIF mRNA was detected by real-time quantitative PCR. MIF protein level was detected by Western blotting. Cell proliferation was examined by MTT assay. Cell colony formation rate was tested by flat-plate colony formation experiment. Results The level of miR-451a was low and MIF mRNA was higher in liver cancer tissues. The luciferase reporter system showed that the intensity of the fluorescent signal was clearly weaker in MIF 3'UTR wild-type co-transfected cells with miR-451a mimics as compared with the other transfection groups. When HepG2 cells were infected with the lentivirus over-expressing miR-451a, the expression of miR-451a significantly increased; the expression of MIF significantly decreased; the cell proliferation and colony formation ability were weakened. Conclusion Overexpression of miR-451a can inhibit cell proliferation and colony formation by inhibiting MIF expression in HepG2 cells.