Abstract: Escherichia coli are most common pathogen from a contaminated environment in lactating dairy cows. For investigating the changes of plasma protein form E. coli infected cows and exploring the mechanism of host defense, such changes were examined using an integrated proteomic approaches consisting of plasma protein and minor abundance protein enrichment by ProteoMiner kit, protein separation by two-dimensional gel electrophoresis, stained with Coomassie Blue G-250 solution, and protein identification by HPLC equipped with ion trap mass spectrometer. The results showed that the nineteen protein spots were changed in cows infected with E. coli mastitis, and fifteen spots were identified as seven proteins. Haptoglobin, alpha 1 acid glycoprotein, and serum amyloid protein A were up-regulated in plasma from E. coli infected cows. Expression of haptoglobin by ELISA method was significantly higher in E. coli infected cows than in healthy controls(P<0.01), E. coli infected cows altered the plasma protein level, and suggested that changes of proteins may be useful to clarify the host defense mechanisms and response to invasion of mammary tissues by E. coli infection, and potential protein targets for diagnose and treatment.