Aim To investigate the action of estrogen receptor in Genistein upregulating the expression of endothelial nitric oxide synthase(eNOS)in endothelial cells.Methods Human umbilical vein endothelial cells were exposed to medium or oxide low density lipoprotein(ox-LDL)(100 mg/L)in the presense or absence of estrogen antagonists ICI182780(1 μmol/L)or/and actinomycin D(5 mg/L)for 0.5 hour,then were treated with Genistein(100 nmol/L)for 24 hours.The mRNA expression of eNOS was detected by real-time PCR,the protein expression of eNOS was determined by Western Blotting.Results ox-LDL downregulated the expression of eNOS mRNA and protein(P><0.05 vs that of basal level);Genistein upregulated the expression of eNOS mRNA and protein(P><0.05 vs that of ox-LDL-treated group),furthermore,the increase can be inverted by estrogen antagonists ICI182780 or actinomycin D(P><0.05).Conclusion Genistein could upregulate the expression of eNOS,which is associated with estrogen receptor regulating genes transcription.