Abstract： Objective To evaluate the effect of endoplasmic reticulum stress in trophocytes,in patients with intrahepatic cholestasis of pregnancy (ICP).Methods Sixty-one pregnant women who were hospitalized in Women's Hospital,School of Medicine,Zhejiang University from January to December 2015 were recruited.Thirty-one women who were diagnosed as ICP were defined as the ICP group and 30 healthy pregnant women were defined as the control group.The localization and expression intensity of glucose regulated protein 78 (GRP-78) in placental tissues were detected by immunohistochemistry technique.Electronic microscope was used to observe ultra-microstructure change of the endoplasmic reticulum in trophocytes and cell line Swan71.Reverse transcription (RT)-PCR and western blot were used to investigate the expression of GRP-78 mRNA and protein in Swan 71 cell.Results (1) GRP-78 protein was mainly expressed in the cytoplasm of cytotrophoblasts and syncytiotrophoblasts.The protein expression of GRP-78 in placentas of the ICP group (13.2±2.4) was significantly higher than that in the control group (7.8±1.3,P＜0.01).(2) The volume of endoplasmie reticulum did not increase and the microvilli developed well,with no swelling and no expansion of endoplasmic reticulum in the control group.In the ICP group,microvilli injury,endoplasmic reticulum edema were found;the volume of endoplasmic reticulum increased,with dilation,vacuolation and significant degranulation.After treated with 100 μmol/L cholyglycine for 24 hours,universal dilatation of the endoplasmic reticulum were seen in the Swan71 cells.(3) In Swan71 cells,cholylglycine displayed a concentration-dependent up-regulation on the expression of GRP-78.The expressions of GRP-78 mRNA in 0,25,50,100 μmol/L cholylglycine experimental group were 1.01±0.17,2.17±0.16,5.47±0.36,5.65 ± 0.82,respectively.The expression of GRP-78 protein in 0,25,50,100 μmol/L cholylglycine experimental group were 1.01±0.04,1.17±0.15,1.33±0.13,1.73±0.13,respectively.The expression of GRP-78 mRNA and protein in 100 and 50 μ mol/L cholylglycine experimental group were significantly higher than 0 μmol/L (all P＜0.01).Conclusion The obvious expansion of endoplasmic reticulum and the increased expression of GRP-78 in trophocytes indicated that endoplasmic reticulum stress of trophocytes may be involved in the pathogenesis of ICP.