A gene coding for thermotolerant beta-xylosidase from Aspergillus sp. BCC125 was characterized. The recombinant enzyme was expressed in methylotrophic yeast Pichia pastoris KM71 and especially high yield of secreted enzyme was obtained. beta-xylosidase possessed high enzyme efficiency (K-cat/K-m = 198.8 mM(-1) s(-1)) toward pNP-beta-D-xylopyranoside (pNP beta X) with optimal temperature and pH for activity of 60 degrees C and pH 4.0-5.0, respectively. The identified beta-xylosidase showed clear synergism with previously identified xylanase for hydrolysis of xylan in vitro as well as simultaneous saccharification and fermentation process (SSF) in vivo with Pichia stipitis. (C) 2012 Elsevier Ltd. All rights reserved.