The stress-inducible immediate early response gene X-1 (IEX-1) regulates cell proliferation and apoptosis in a cell type and stimulus-dependent manner. The aim of this study was to investigate IEX-1 expression in preeclampsia placenta and human umbilical vein endothelial cells (HUVECs) cultured in the serum isolated from preeclampsia patients, to explore its relationship with the pathogenesis of preeclampsia. Thirty preeclampsia patients with 10 cases in the moderate group, 20 cases in the severe group (PE group) and 20 cases of normal pregnant women (control group) were randomly obtained. Reverse transcriptase-polymerase chain reaction and immunohistochemistry showed that IEX-1 expression was significantly higher in preeclampsia patients than in normal pregnant women (p < 0.05). There was also a significant difference between moderate and severe preeclampsia (p < 0.05). IEX-1 protein was mainly present in cytoplasm of placental trophoblast cells and decidual cells. Compared with the normal pregnancy group, IEX-1 in the preeclampsia group was colored more obviously, and the color was strengthened in correlation with the severity of the disease using immunocytochemial method. Flow cytometry and MTT revealed that the serum isolated from preeclampsia patients appeared to promote IEX-1 expression in cytoplasm of HUVECs, inhibited the proliferation and promoted the apoptosis of HUVECs when compared to the serum of normal pregnant women. Our study demonstrates a correlation of IEX-1 expression levels with the severity of preeclampsia. Given a well-known function of IEX-1 in regulation of apoptosis, IEX-1 may be important in the pathogenesis of preeclampsia by regulating placental villous trophoblast and decidual cell apoptosis as well as participation in endothelial cell injury process.