Abstract: The aims of this study were to investigate the effects of injecting low dose bacterial lipopolysaccharide (LPS) into external pudic artery on plasma proteins in lactating dairy cow, and explore the mechanism of host response to LPS challenge. All 6 cows were injected LPS(0.01 μg·kg-1 body weight). Twodimensional electrophoresis gel (2DE) coupled with MALDITOFTOF spectrometry was used. Plasma proteins at 0, 6, 12 and 24 h after LPS injecting were separated by twodimensional electrophoresis. After visualization proteins with Coomassie Brilliant Blue G250, the different protein spots were detected by PDQuest 8.0.1 software and differential proteins were identified by MALDITOFTOF spectrometry. The result showed that milk SCS started to increase after injecting LPS and peaked at 6 h, and then gradually decreased to the level before injecting LPS at 24 h. Eight protein spots were identified to be four proteins including vitamin Dbinding protein precursor, serpin A36, alpha1 antitrypsin and serpin A31 precursor. These protein expression levels were upregulated at 6, 12 and 24 h in cows after injecting LPS, but there was not significantly different among 6, 12 and 24 h. Vitamin Dbinding protein precursor, serpin A36, alpha1 antitrypsin and serpin A31 precursor play important roles in immune response, the identification of this proteins may be helpful to elucidate the molecular mechanism of host response to LPS challenge.