Two parts of xylanases(Part A and Part B) were separated and purified from a culture filtrate of Trichoderma reesei Rut C30 by ammonium sulfate precipitation,followed by DEAESephadex A50 and SPSephadex C50 column chromatography.Part A and Part B were further purified to homogeneity by Sephadex G100 column chromatography.The molecular weights of Part A and Part B were estimated to be 20 300 and 13 500 by SDSPAGE chromatography.The optimal reaction conditions for Part A and Part B were at 45 ℃,pH 4.5,and at 55 ℃,pH 5.5,respectively.Part A was stable in a pH range from 3.0 to 5.5,while Part B was stable in a pH range from 3.5 to 7.5.The major products of enzymatic hydrolysis with Part A were xylooligosacchrides,with a small amount of xylose,while that with Part B were merely xylooligosacchrides.