Objective：To explore the expression of quiescin sulfhydryl oxidase 1（QSOX1） in the placentas of preeclampsia（PE），its effects on the apoptosis and proliferation of trophoblast cells and its probable role in the development of PE. Methods：Human term placentas from normal pregnancies（31 cases） and from pregnancies complicated by PE（35 cases） were obtained，and all samples col－lected in the First Affiliated Hospital of Chongqing Medical University from November 2015 to December 2016. Under the condition of normal oxygen，human transformed primary extravillous tro－phoblast cell line（HTR8/SVneo） cells were divided into the small interference RNA（siRNA） group，the negative control group（siControl） and the QSOX1 inhibition group（siQSOX1），and the experiment repeated 3 times，6 samples in each group. Under the condition of hypoxia，HTR8/SVneo cells were divided into 4 groups respectively，the normal oxygen treatment group（0 h），the 6 hour hypoxia treatment group（6 h），the 12 hour hypoxia treatment group（12 h） and the 24 hour hypoxia treatment group（24 h），and the experiment repeated 3 times，6 samples in each group. Western blot was used to detect the expression levels of QSOX1 in the placen－tas from normal pregnant women and from PE pregnant women，and the expression levels of QSOX1 and hypoxia inducible factor-1α（HIF-1α） in human transformed primary extravillous trophoblast（HTR8/SVneo） cells treated with hypoxia. Down-regulation of QSOX1 in HTR-8/Svneo cells was achieved by small interfering RNA（siRNA） interference. The protein expression levels of cleaved cysteinyl aspartate specific proteinases（Cleaved caspase） and CyclinD1 in HTR-8/Svneo cells treated with siRNA were measured by Western blot. Furthermore，the apoptosis of transfected cells was detected by flow cytometry，and the cell proliferation by colorimetric method. Results：QSOX1 was overexpressed in the PE placenta compared with the normal placenta（0.955±0.285 vs. 3.921±0.960） （P=0.001）. Hypoxia induced the higher expressions of QSOX1 and HIF-1α in HTR-8/Svneo cells（1.183±0.160 vs. 3.987±0.098；1.051±0.444 vs. 1.912±0.118）（P=0.000）. Inhibition of QSOX1 expression in HTR-8/Svneo cells led to the decreased expressions of Cleaved caspase-3 and Cleaved caspase-9（2.940±0.514 vs. 1.075±0.121；9.223±1.230 vs. 1.011±0.019）（P=0.004，P=0.000），but the elevated expression of CyclinD1（1.851±0.972 vs. 4.189±0.399） （P=0.018）. Inhibition of QSOX1 expression in HTR-8/Svneo cells attenuated the cell apoptosis[（21.007±2.214）% vs. （10.057±0.388）％]（P=0.001） but promoted the cell proliferation （0.389±0.162 vs. 1.401±0.059）（P=0.020）. Conclusion：Overexpression of QSOX1 may be involved in the pathogenesis of PE by regulating the apoptosis and proliferation of trophoblast cells.