This study investigated the role and mechanism of Cdc42 in Endothelin-1 (ET-1)-induced trophoblast cell migration.We examined ET-1-mediated stimulation of trophoblast migration with HTR-8/SVneo cells. Cdc42 activation was measured after ET-1 treatment of HTR-8/SVneo cells. To determine the ET receptor subtype involved in ET-1-mediated Cdc42 activation, experiments were performed in the presence of ET A and ET B receptor antagonists. Finally, using siRNA we knocked down the expression of Cdc42 to examine the involvement of Cdc42 in the regulation of ET-1-stimulated trophoblast cell migration.ET-1 was shown to have a dose-dependent effect on trophoblast migration. At low concentrations of ET-1 (0.1 nmol/L) ET-1 had a stimulatory effect on cell migration. ET-1 (10 nmol/L) increased HTR-8/svneo cell migration index by 2.5 fold. ET-1 (10 nmol/L) elevated protein level and activity of Cdc42. ET-1 induced activation of Cdc42 GTPase was mediated by both ET A and ET B . ET-1-induced cell migration was shown to be inhibited by Cdc42 siRNA.The inhibition was not mitigated by the addition of ET-1, suggesting that Cdc42 plays an important role in trophoblast migration and is obligatory for ET-1 action.ET-1 stimulates EVT migration through Cdc42 activation.