An extracellular chitinase and a chitin-binding protein(CBP21) were isolated from the culture of Serratia marcescens and purified to electrophoretic homogeneity by ordinal procedures containing ammonium sulfate precipitation,DEAE-Sepharose and Phenyl-Sepharose chromatography.Their relative molecular masses were estimated to be respectively about 58kD and 21kD by SDS-PAGE.CBP21 had great synergistic effect with the chitinase on chitin hydrolysis.The optimum temperature and pH for the enzyme activity were 50℃ and 6.5 respectively.The enzyme activity was stable under 55℃ and in the pH range of 4.5～8.0.Michaelis constants of the enzyme were Km 0.22 mg/mL and Vm 1.26 μmol/(min·mg) respectively.The activity was enhanced by K+,Sn2+ and Mn2+ and was strongly inhibited by Pb2+,Hg2+ and Cu2+.EDTA and 2-mercaptoethanol(2-ME) enhanced the activity by 65% and 105% respectively.H2O2 strongly inhibited chitinase activity,which indicated that hydrosulfide group was the possible essential residue for enzyme activity.