Objective:To evaluate the role of O-sialoglycoprotein endopeptidase (OSGEP) in hepatic ischemia-reperfusion injury (HIRI) and the relationship with oxidative stress in mice.Methods:Experiment Ⅰ Twenty-four SPF healthy male C57BL/6 mice, 12 wild-type and 12 OSGEP knockdown, aged 6-8 weeks, weighing 18-22 g, were divided into 4 groups ( n=6 each) by the random number table method: wild-type shamoperation group (Sham group), wild-type HIRI group (HIRI group), OSGEP knockdown+ sham operation group (Sham+ KD group) and OSGEP knockdown+ HIRI group (HIRI+ KD group). Ischemia-reperfusion model was prepared by blocking the hepatic artery and portal vein for 60 min followed by reperfusion in anesthetized animals, the blood vessels were only exposed without occlusion in Sham group and Sham+ KD group, and the blood vessels were clamped for 60 min followed by reperfusion in HIRI group and HIRI+ KD group. The mice were sacrificed after 6-h reperfusion to extract liver tissue samples for microscopic examination of histopathological changes (with an optical microscope after HE staining) which were evaluated using Suzuki score and for determination of the serum concentrations of alanine aminotransferase (ALT) and aspartate aminotransferase (AST), level of reactive oxygen species (ROS) (using the DCFH-DA fluorescent probe method), contents of malondialdehyde (MDA) and glutathione(GSH) in liver tissues (using a colorimetric method) and expression of OSGEP (using Western blot). Experiment Ⅱ The well-growing AML12 cells were divided into 4 groups ( n=30 each) using a random number table method: control group (C group), oxygen-glucose deprivation/restoration (OGD/R) group, OGD/R+ OSGEP knockdown group (OGD/R+ KD group), and OGD/R+ OSGEP knockdown negative control group (OGD/R+ NC group). Group C was cultured under normal conditions. Group OGD/R was subjected to O 2-glucose deprivation for 6 h followed by restoration of O 2-glucose supply for 24 h in OGD/R group. In OGD/R+ KD group, stable transfection of AML12 cells with OSGEP knockdown was performed prior to the experiment, and the other procedures were the same as those previously described. The cell survival rate was measured by the CCK-8 assay, the release of lactate dehydrogenase (LDH) was measured, the DCFH-DA method was used to detect the levels of ROS, and the contents of MDA and GSH were determined using a colorimetric method. Results:Experiment Ⅰ Compared with Sham group, the expression of OSGEP was significantly down-regulated, the serum concentrations of AST and ALT, Suzuki score, levels of ROS and content of MDA were increased, and the GSH content was decreased in HIRI group ( P<0.05), and no significant change was found in each parameter in Sham+ KD group ( P>0.05). Compared with HIRI group, the serum concentrations of AST and ALT, Suzuki score, levels of ROS and content of MDA were significantly increased, and the GSH content was decreased in HIRI+ KD group ( P<0.05). Experiment Ⅱ Compared with group C, the expression of OSGEP was significantly down-regulated, the cell survival rate and GSH content were decreased, and the release of LDH, levels of ROS and content of MDA were increased in group OGD/R ( P<0.05). Compared with OGD/R group, the cell survival rate and GSH content were significantly decreased, and the release of LDH, levels of ROS and content of MDA were increased in OGD/R+ KD group ( P<0.05), and no significant change was found in each parameter in OGD/R+ NC group ( P>0.05). Conclusions:OSGEP plays an endogenous protective role in HIRI by inhibiting oxidative stress in mice.