Corn stover was treated with NaOH, NaOH + anthraquinone (AQ), NaOH + Na2SO3 (alkaline), NaOH + Na2SO3 (neutral), and NaOH + Na2S, respectively. The treated corn stover was subjected to hydrolysis with cellulase (20 FPU/g dry biomass) and beta-glucosidase (10 IU/g dry biomass). Compared with other pretreatment methods, alkaline sodium sulfite pretreatment (ASSP) at a relatively low temperature of 140 degrees C provided for the best lignin removal of about 92%. After ASSP with 10 wt.% of the total alkali charge (Na2SO3:NaOH = 1:1) at 140 degrees C for 30 min and subsequent enzymatic hydrolysis, a total sugar yield of 78.2% was obtained on the basis of the amount of glucose and xylose released from raw corn stover. This yield was 24.0% higher than that achieved with NaOH only under the same conditions. Therefore, the supplement of Na2SO3 in alkali pretreatment can facilitate delignification and significantly improve the enzymatic saccharification. (C) 2012 Elsevier Ltd. All rights reserved.