A xylanase gene, xynf11a of Aspergillus fumigatus MKU1 was cloned and expressed in Pichia pastoris X33. Two exons of the xynf11a gene were amplified separately and fused by overlap extension PCR. The fused product was cloned in yeast expression vector pPICZB and expressed in P. pastoris under the control of the AOX1 promoter. A pastoris transformants expressing recombinant xylanases were selected on xylan agar plate and their ability to produce the xylanase was evaluated in flask cultures. P. pastoris X33 (pZBxynf11aFP) efficiently secreted the recombinant xylanase into the medium and produced the high level of xylanase activity (14 U/ml) after 96 h of growth. The recombinant xylanase produced by P. pastoris showed maximum activity at pH 6.0 and temperature 60 degrees C. The recombinant xylanase did not exhibit any cellulase activity and hence it could be potentially used for pretreatment of paper pulp before bleaching. (C) 2009, The Society for Biotechnology, Japan. All rights reserved.