Extracellular β-xylosidase (1,4-β-D-xylan xylohydrolase, EC 22.214.171.124) from culture filtrates of Neurospora crassa was purified to homogeneity by preparative isoelectric focusing followed by gel electrophoresis. The molecular weight of the purified xylosidase was 83,000 D and the Km on p-nitrophenyl-β-D-xyloside was 0.047mM. The homogeneous xylanase (1,4-β-D-xylan xylanohydrolase, EC 126.96.36.199) and β-xylosidase showed differences in their mode of action towards xylooligosaccharides. The degree of hydrolysis of D-xylan by xylanase of N. crassa was 18%. Supplementation of β-xylosidase from the same organism resulted in 48% hydrolysis. The synergistic effect was more pronounced, with the hydrolysis of 68%, when a homogeneous preparation of β-xylosidase from Sclerotium rolfsii was added to the saccharification system.