Abstract: Extraction of corncob xylan with steam flash-explosion assisted by dilute sulfuric acid presoaking was investigated, with the xylan extraction rate and average degree of polymerization (DP) as the evaluating index. Optimum conditions were:dilute sulfuric acid concentration of 0.1% (w/v) , steam pressure of 1.8MPa and pressure maintaining time of 3min. The corresponding extraction rate of corncob xylan reached 22.33% and an amount of xylo-oligosaccharides (XOs) of 39.96% (based on the total soluble sugar) was produced. The extract was hydrolyzed by endo-xylanase and the content of XOs in hydrolysate was 65.08% (based on the total soluble sugar) .