Bacillus thermantarcticus, a thermophilic bacterium isolated from Antarctic geothermal soil near the crater of Mount Melbourne, produced extracellular xylanase (1,4-β-d-xylan xylanohydrolase; E.C. 3.2.1.8) and β-xylosidase (1,4-β-d-xylan xylohydrolase; E.C. 3.2.1.37). Each extracellular enzyme was separated by gel filtration with Sephacryl S-200 and further purified to homogeneity (119-fold for xylanase and 160-fold for β-xylosidase). The optimum temperatures were 80 o C for xylanase at pH 5.6 and 70 o C for β-xylosidase at pH 6.0. The isoelectric points and molecular masses were 4.8 and 45 kDa for xylanase and 4.2 and 150 kDa for β-xylosidase, respectively. Xylanase was stable at 60 o C for 24 h, whereas it showed a half life at 70 o C of 24 h and at 80 o C for 50 min. β-xylosidase activity did not decrease after 1 h at 60 o C. Km of xylanase for xylan was 1.6 mg/ml, Km of β-xylosidase for p-nitrophenyl-β-d-xylopyranoside was 0.5 mM and for o-nitrophenyl-β-d-xylopyranoside was 1.28 mM. The action of two enzymes on xylan gave only xylose.