Objective To study the effect of safflower yellow(SY) on the proliferation of vascular smooth muscle cells (VSMC) and the underlying mechanism.Methods The effects of SY on the proliferation of VSMC and the tyrosine protein kinase (TPK) activity in VSMC were studied by means of cell count and 32 P-incorporation in cultured rabbit VSMC of passages 4 ～ 8.Results The proliferation of serum-stimulated VSMC was inhibited by SY in a dose- and time-dependent manner.The maximum inhibition rate (54.6%) was obtained on the 3rd day of incubation when SY was increased to 1.0g/L.When SY was set at 1.0g/L,the inhibition reached its climax (52.0%) on the 4th day.The TPX activity in serum-stimulated VSMC,which was also inhibited by SY,decreased with the increasing concentration of SY within a certain a certain range,with the maximum inhibition rate (97.8%) attained in the presence of SY 1.0 g/L on the 3rd day.Conclusion SY inhibits the proliferation of serum-stimulated VSMC,which may involve the role of TPK.