Abstract: OBJECTIVE To study the effect of neferine on the proliferation and phenotypic modulation of human umbilical vein smooth muscle cells (HUVSMCs) cultured in vitro. METHODS The effect of neferine(0.1, 0.5, 1.0, 5.0 μmol·L^-1) on HUVSMCs proliferation was studied by using MTT colorimeter and flow cytometry. Western blotting was used to indicate the changes of protein levels of the contractile-phenotype smooth muscle specific markers, such as smooth muscle myosin heavy chain-1 (SM1), calponin 1 and α-actin. RESULTS Neferine could significantly decrease the cell numbers of HUVSMCs after treatment for 12, 24, 48 h, and the anti-proliferation effects were in a concentration-dependent and time-dependent manner when the concentrations of neferine were between 0.1 and 5.0 μmol·L-1. In the absence of neferine treatment, the protein levels of the smooth muscle specific markers (SM1, calponin 1 and α-actin) decreased during culture. However, the treatment of VSMCs with neferine (0.5 or 5.0 μmol·L^-1) for 48 h reversed the effect in a concentration-related manner. CONCLUSION These data suggest that neferine may arrest the growth of VSMCs and inhibit phenotypic modulation, thereby preventing cell dedifferentiation. These properties of neferine suggest that the drug can provide useful therapy for atherosclerosis and restenosis.