Abstract: Xylo-oligosaccharides derived from xylan have a high application potential in food and pharmaceutical industries. As an agricultural by-product, corn stover with high hemicellulose content is an important raw material for biorefinery. In order to broaden the raw material source of xylo-oligosaccharides, the work was carried out to investigate the effect of alkali extraction conditions on the quality of xylan. NaOH mass concentration and extraction temperature were selected to study their influence on yield, purity and structural characteristics of xylan. The de-waxed corn stover was treated with NaOH solution of 4, 6, 8, 10, 12, 16, 20 and 24wt% at 121 ℃ for 2 h with a constant solid-liquid ratio of 1:10 (g/mL). The extracts were neutralized to the pH value of 5.0 with the concentrated HCl, and then concentrated under vacuum. Xylan was precipitated from the filtrate by adding the ethanol with the volume of 3 times and then freeze-dried. The remained extracts were freeze-dried and the alcohol-soluble lignins were obtained. The components of the xylan, alkali-insoluble residues and alcohol-soluble lignins were determined by the National Renewable Energy Laboratory. The extractability and structural characteristics of xylan were elucidated by gel permeation chromatography (GPC) techniques. The results demonstrated that xylan isolated with different alkali concentrations presented different chemical compositions and structural characteristics. The alkalinity played an important impact on cleaving the chemical linkages between hemicellulose and lignin. The recovery of xylan increased first and then decreased following the increasing alkali concentration with a maximum value at 10%. At the optimum NaOH concentration, the recovery and purity of xylan were 76.20% and 59.35%, respectively. The weight average molecular weight of xylan decreased from 48.62 to 32.02 kD with alkaline concentration increasing. A high alkaline concentration could degrade a considerable amount of hemicellulose. Based on the molecular mass distribution data of xylan, it could be speculated that the xylan was partly linked covalently with lignin to form the lignin-carbohydrate complex (LCC). Moreover, the alkali-insoluble residues mainly contained cellulose, and the cellulose content increased with the alkali concentration increasing. An experiment process similar to alkaline extraction was used to study the influence of extraction temperature on xylan. The de-waxed corn stover was treated in 10% NaOH solution for 2 h with a solid-liquid ratio of 1:10 (g/mL) at 30, 60, 80, 90, 100, 110 and 121 ℃. The results demonstrated that NaOH concentration was a more obvious factor affecting xylan than temperature. The trend of xylan recovery with the temperature was the same as alkaline concentration. The curve of xylan recovery ratio between 60 and 110 ℃ was stable. When the temperature was 121 ℃, a decrease of recovery ratio appeared. It indicated that the high temperature may have an adverse effect on the recovery of xylan. The xylan obtained under different temperature differed from each other in color value. When the temperature was higher than 90 ℃, the xylan color value increased due to Maillard reaction. Taking into account the effect of temperature on the composition and quality of xylan, 90 ℃ was selected as the optimum extraction temperature. Therefore, the optimal extraction conditions were the NaOH concentration of 10% and the reaction temperature of 90 ℃, under which the xylan dissolution ratio, yield and purity were 86.37%, 76.92% and 63.90% respectively. GPC spectrums showed that the weight average molecular weight of xylan increased first and then decreased with the temperature increasing; the trend was identical with the change of the recovery of xylan. The polydispersity coefficient of xylan increased from 5.60 to 7.38 with temperature increasing from 30 to 121 ℃. The results provide a theoretical basis for further improving the recovery ratio and quality of corn stover xylan and realizing the sustainable utilization of corn stover.