In order to detect the expression of RhoA in placenta from normal pregnancy and preeclampsia and evaluate the role of RhoA in preeclampsia, the expression of RhoA in placenta collected from 40 preeclampsia patientsand 20 normotensive controls was determined by immunohistochemistry and RT-PCR. RhoA was found in syncytiotrophoblasts and cytotrophoblasts. The mean density of RhoA protein in placental tissues of mild and severe preeclampsia groups was significantly higher than that in normal pregnancy. The expression level of RhoA mRNA in mild and severe preeclampsia groups was significantly higher than that of normal pregnancy. Increased expression of RhoA in placental tissues might play an important role in the pathogenesis of preeclampsia.