Aim To investigate the effect of genistein on activation of nuclear factor kappa B(NF-κB) in vascular smooth muscle cells(VSMC) induced by oxidized low density lipoprotein(ox-LDL) and further examine the activation mechanism. Methods Human umbilical vein smooth muscle cells were pretreated with genistein in different concentrations(10,30,90 μmol/ L) and then treated by 50 mg/ L of ox-LDL for 2 hours.Immunocytochemistry staining was used to detect the nuclear translocation of NF-κB subunit p65.The intracellular level of inhibitory kappa B(IκB),inhibitor of NF-κB,was detected by Western blotting analysis.The levels of nitric oxide(NO) in the culture medium was detected by the method of nitric acid reductase. Results Genistein significantly restrains the nuclear translocation of NF-κB in VSMC induced by ox-LDL;High concentration of genistein increases intracellular IκB-α level and doesn't have significant effect on level of NO in the culture medium. Conclusion Genistein inhibited activation of NF-κB induced by ox-LDL in VSMC.The mechanism is associated with increase of IκB and may not associate with nitric oxide level.