Abstract: In order to increase xylooligosaccharides in the enzymatic hydrolysate with a degree of polymerization(DP) between 2 and 5, crude xylanase was ultrafiltrated to hydrolyze hightemperature degraded xylan The results showed that three xylanase components, named xylanase A (MW 30—50 ku), xylanase B (MW 10—30 ku) and xylanase C (MW＜10 ku), were obtained after ultrafiltration fraction of crude xylanase. These xylanase components were able to hydrolyze the hightemperature degraded xylan efficiently to xylooligosaccharides with a DP between 2 and 5 Xylanase B performed much better than xylanase A and C; 1 mg protein of xylanase B could produce xylobiose 263 g, xylotriose 185 g, xylotetraose 115 g and xylopentaose 046 g