Xylaria regalis, a wood-grown ascomycete isolated in Taiwan, produces beta-glucosidase (EC 3.2.1.21) extracellularly, The beta-glucosidase was purified to homogeneity by ammonium sulfate precipitation, ion-exchange, and gel filtration chromatography. The molecular mass of the purified enzyme was estimated to be 85 kDa by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. With p-nitrophenyl beta-D-glucopyranoside (PNPG) as the substrate at pH 5.0 and 50 degrees C, the K-m was 1.72 mM and V-max was 326 mu mol/min/mg. Optimal activity with PNPG as the substrate was at pH 5.0 and 50 degrees C. The enzyme was stable at pH 5.0 at temperatures up to 50 degrees C, The purified beta-glucosidase was active against PNPG, cellobiose, sophorose, and gentiobiose, but did not hydrolyze lactose, sucrose, Avicel, and o-nitrophenyl beta-D-galactopyranoside. The activity of beta-glucosidase was stimulated by Ca2+, Mg2+, Mn2+, Cd2+ and beta-mercaptoethanol, and inhibited by Ag+, Hg2+, SDS, and p-chloromercuribenzoate (PCMB).