Abnormal placenta trophoblast proliferation and apoptosis is related to the pathogenesis of preeclampsia.Emerging evidence has also indicated that key pregnancy-associated hormones, such as hCG,progesterone, are found in high concentration at the maternal-fetal interface.The purpose of this study was to investigate the expression of CYP11A, a key enzyme in steroid hormone synthesis and metabolism, in normal pregnancy and severe preeclampsia placenta and to explore the underlying mechanism of the relationship between the altered CYP11A expression and onset of preeclampsia.