The method of chemical modification was used to modify lysozyme in this study. With EDAC as condensing agent,cinnamic acid,caffeic acid and p-coumaric acid as modifier,a certain degree of modified enzyme was formed. The properties of the modified enzymes were studied. Results showed that the lytic activity of modified enzyme declined slightly,but the modified enzyme expanded the bactericidal spectrum to the Escherichia coli and Pseudomonas aeruginosa. The minimal inhibition concentrations of caffeic acid and p-coumaric acid modified enzyme were both 0. 5 mg /mL,and that of cinnamic acid modified enzyme was 0. 75 mg /mL. However,the efficacy for Staphylococcus aureus and Micrococcus lysodeikticus was reduced slightly,the minimal inhibition concentrations of caffeic acid and p-coumaric acid modified enzyme for themwere both 1. 25 mg /mL,and that of cinnamic acid modified enzyme was 1. 25 mg /mL and 1. 50 mg /mL,The secondary structures of these three modified enzymes had some changes.