Two endo-1,4-beta-zylanases (m. w. 24,000 and 41,000) and six exo-1,4-beta-xylosidases, differing in their molecular weights and isoelectric points, were found in a xylanase preparation from Aspergillus niger, using different methods of fractionation. An electrophoretically homogeneous exo-1,4-beta-xylosidase (m. w. 30,000) purified 120-fold, with pI 4.6, having optimal effect on methyl-beta-D-xyloside at pH 3.0 was obtained. Exo-1,4-beta-xylosidase splits off xylose from the ends of the xylan chains at xylotriose, xylobiose and methyl-beta-D-xyloside and is characterized by a high transglycosilase activity. An electrophoretically homogeneous endo-1,4-beta-xylanase (m. w. 24,000) purified 250-fold, with pI 4.2 and optimal effect on carboxymethylxylan at pH 4.2 was isolated. Endo-1,4-beta-xylanase splits arabinoglucuronoxylan to form xylooligosaccharides; however, it does not hydrolyze xylobiose.