A putative endo-1,4-beta-d-xylanohydrolase gene xyl10 from Aspergillus niger, encoding a 308-residue mature xylanase belonging to glycosyl hydrolase family 10, was constitutively expressed in Pichia pastoris. The recombinant Xyl10 exhibited optimal activity at pH 5.0 and 60 A degrees C with more than 50 % of the maximum activity from 40 to 70 A degrees C. It retained more than 90 % of the original activity after incubation at 60 A degrees C (pH 5.0) for 30 min and more than 74 % after incubation at pH 3.0-13.0 for 2 h (25 A degrees C). The specific activity, K (m) and V (max) values for purified Xyl10 were, respectively, 3.2 x 10(3) U mg(-1), 3.6 mg ml(-1) and 5.4 x 10(3) mu mol min(-1) mg(-1) towards beechwood xylan. The enzyme degraded xylan to a series of xylooligosaccharides and xylose. The recombinant enzyme with these properties has the potential for various industrial applications.