The purpose of this study was to investigate the expression of estradiol and estrogen receptor α (ESRα) in severe preeclamptic (sPE) pregnancies compared with normal pregnancies. Sera and placentas were obtained from i) patients with sPE (n=25) and ii) a normal control group (n=25) who underwent elective Cesarean deliveries. Estradiol expression was assessed by enzyme-linked immunosorbent assays (ELISAs). ESRα expression was assessed by reverse transcription polymerase chain reaction (RT-PCR) analysis and western blot analysis. In preeclamptic pregnancies, estradiol was underexpressed (P<0.05), however, ESRα mRNA and protein levels were increased significantly in comparison with normal pregnancies (P<0.05). These results show that estradiol and ESRα are deregulated in preeclamptic pregnancies, which in turn suggests the involvement of these molecules in the pathogenesis of preeclampsia.