An extracellular beta-glucosidase was extracted from the culture filtrate of Aspergillus niger No. 5.1 and purified to homogeneity by using ammonium sulfate precipitation, Chitopearl-DEAE chromatography, and Sephadex G-100 chromatography. The specific activity of the enzyme was enriched 6.33-fold, with a recovery of 11.67%. The enzyme was a monomer and the molecular mass was 67.5 kDa by sodium dodecyl sulfate polyacrylamide gel electrophoresis and 66.5 kDa by gel-filtration chromatography. The enzyme had optimum activity at pH 6.0 and 60 degreesC and was stable over the pH range of 3.0-9.0. It showed specificity of hydrolysis for p-nitrophenyl-beta-D-glucoside and cellobiose. The K-m and V-max values of the enzyme for cellobiose and salicin were 5.34 mM, 2.57 mumol/(mL.s), and 3.09 mM, 1.34 mumol/(mL.s), respectively. Both amino acid composition and N-terminal amino acid sequence of the enzyme were determined, which provides useful information for cloning of this enzyme.