Objective To detect the expression of human endogeneous retrovirus family W env1 (HERVWE1) in placentas of normal pregnant women and patients with preeclampsia and explore its role in the pathogenesis of preeclampsia.Methods Fifty-two cases of placental tissues provided by Shandong Maternity Hospital were from iodine deficiency areas (county or city:.Zhangqu, Changqing, Pingyin) of Shandong Province, including 30 cases of preeclampsia placentas as case group, 22 cases of normal term pregnancy placentas as control group.The mRNA expression of HERVWE1, human chorionic somator mammotropin (HCS), chorionic specific transcription factor (GCMa) and amino acyl carrier 2 (ASCT-2) in placentas of the two groups were determined by real-time PCR, and the protein expression of HERVWE1 was determined by Western blotting.Results The mRNA expression levels of HERVWE1 (0.149 ± 0.045 vs.0.409 ± 0.028) and HCS (336.600 ± 50.100 vs.815.600 ± 101.300) in placentas of patients with preeclampsia were significantly lower than those in the control group (t =25.60, 20.40,all P ＜ 0.05).There were no significant difference in GCMa (0.022 ± 0.007 vs.0.024 ± 0.009) and ASCT-2 (0.423 ± 0.050 vs.0.438 ± 0.060) between the two groups (t =0.87, 0.95, all P ＞ 0.05);Western blotting analysis showed that expression of HERVWE1 protein (0.340 ± 0.010 vs.0.580 ± 0.010) in placentas of the case group was lower than that in normal pregnant women (t =85.50, P ＜ 0.05).Conclusion The expression of HERVWE1 is significantly decreased in placentas of the case group and is associated with pathogenesis of preeclampsia.