Abstract： Objective To investigate the relationship between placental endoglin expression and the pathogenesis of severe preeclampsia (SPE). Methods Forty nine pregnant women with SPE and 40 normal pregnant controls were collected in Peking University First Hospital from January 2006 to January 2008,among which,nine SPE patients complicated with fetal growth restriction (FGR),six with hemolysis,elevated liver enzymes and low platelets syndrome (HELLP syndrome) and 12 with heavy proteinuria. The expression of placental endoglin was detected and semi-quantified by immunohistochemistry.Data were analyzed by independent sample t test. Results Endoglin was presented on cell membranes of placental syncytiotrophoblasts and vascular endothelial cells. The endoglin density of SPE group was higher than that of control group (0.1621± 0.0029 vs 0.1576 ± 0.0038,t=- 6.367,P＜0.05).No significant difference in endoglin density was found between FGR group and non-FGR group (0.1611±0.0026 vs 0.1623±0.0029,t=1.107,P＞0.05) ; neither did the heavy proteinuria group and non-heavy proteinuria group (0.1611±0.0032 vs 0.1624±0.0027,t=1.350,P＞0.05).The endoglin density of HELLP group was lower than that of non-HELLP group (0.1595±0.0032 vs 0.1625±0.0027,t=2.495,P=0.016). Conclusions The elevated placental endoglin expression might contribute to the pathogenesis of SPE.