Endo-xylanase secreted by the alkaliphilic Bacillus halodurans was immobilized onto an anionic exchange resin via the ionic linkage and the highest immobilized amount was achieved at pH 8. Approximately 0.4 mg of enzyme could be coupled onto 1 g of anionic exchanger. Time courses of the xylooligosaccharides (XOS) produced from corncob xylan indicated that the immobilized enzyme tends to use shorter xylan chains as the substrate and to produce more xylobiose and xylotriose initially. On the contrary, when free enzyme was employed, products at initial stage of the reaction exhibited higher level of oligomers with degree of polymerization greater than 4, suggesting that free xylanase worked on both longer (insoluble) and shorter (soluble) xylan chains. At the end of 24 h reaction, XOS mixture contained a total of 25.2% and 32.5% (w/w) of xylobiose and xylotriose with immobilized xylanase and free xylanase, respectively. The conversions for converting substrate xylan to soluble XOS with immobilized xylanase was determined to be 80.9%, which was lower than the use of free xylanase (99.8%). The combination of free and immobilized xylanase can be employed to further improve the conversion of XOS. (C) 2011 Elsevier Ltd. All rights reserved.