||A native cellobiase (Cba2) secreted by Cellulomonas biazotea was purified from culture supernatant and characterized. Cba2 appeared to be a major cellobiase component in C. biazotea as its enzymatic activity was estimated to represent 30% of the total secretory cellobiase activity. The enzyme was purified following ammonium sulfate precipitation, gel-filtration chromatography, anion-exchange chromatography and reversed-phase high performance liquid chromatography. The purified Cba2 has an apparent molecular mass of 109 kDa as judged by SDS-PAGE and the homogeneity was further confirmed by N-terminal amino acid sequencing. From kinetic studies, the estimated apparent Km values for p-nitrophenyl-β-D-glucopyranoside and cellobiose were 0.025 mM and 0.73 mM, respectively at 37 [degrees celsius][degrees celsius] and pH 7.0. The purified enzyme has a pH optimum of pH 5.8 and the optimum temperature for activity is 70 ℃. In view of the secretory nature of this native cellobiase and that it appeared as a major component of secretory cellobiases in C. biazotea, it would be worthwhile to clone its gene so that excreted recombinant Cba2 may be largely produced to work synergistically with other cellulases on enzymatic degradation of cellulose. The results reported in this thesis would certainly benefit this further cloning work and the characterization of the recombinant Cba2.