In the present study, the effects of 17beta-estradiol (E2) and phytoestrogen alpha-zearalanol (ZAL) on tissue factor (TF) in plasma of ovariectomized (OVX) rats and human umbilical vein endothelial cells (HUVECs) were investigated. OVX rats were injected intramuscularly twice a week with E2 (1mg/kg) or ZAL (1mg/kg) for five weeks. The concentrations of plasma E2 were measured by radioimmunoassay. The TF levels of plasma were assayed by enzyme-linked immunosorbent assay (ELISA). HUVECs were exposed to E2 or ZAL for 48 h. TF protein and mRNA were assayed by ELISA and RT-PCR, respectively. Nuclear proteins of HUVECs opposed to E2 or ZAL for 8 h were extracted to assay transcription factors activator protein-1 (AP-1) and nuclear factor-kappaB (NF-kappaB) by Western blot. Both E2 and ZAL were found to decrease plasma TF levels of OVX rats significantly. E2 or ZAL were also found down-regulate the expression of TF protein and mRNA in HUVECs. Moreover, both E2 and ZAL might decrease AP-1 and NF-kappaB levels. These results suggest that both E2 and ZAL have inhibitory effects on TF in plasma of OVX rats and HUVECs, which may then contribute to their protective effects on cardiovascular diseases.