A new process for pretreatment of lignocellulosic biomass, designated the soaking in ethanol and aqueous ammonia (SEAA) process, was developed to improve hemicellulose preservation in solid form. In the SEAA process, an aqueous ammonia solution containing ethanol is used. Corn stover was treated with 15 wt.% ammonia at 1: 9 solid-liquid ratio (by weight) at 60 degrees C for 24 h with ethanol added at 1, 5, 20, and 49 wt.% (balance was water). The extents by which xylan was solubilized with no ethanol and with ethanol added at 1, 5, 20, and 49 wt.% of the total liquid were 17.2%, 16.7%, 14.5%, 10.4%, and 6.3% of the original xylan, respectively. Thus, at the highest ethanol concentration used the loss of hemicellulose to the liquid phase was reduced by 63%. The digestibility of glucan and xylan in the pretreated corn stover samples by cellulase was not affected by ethanol addition of up to 20 wt.%. The enzymatic digestibility of the corn stover treated with 49 wt.% ethanol added was lower than the digestibility of the sample treated with no ethanol addition. Thus, based on these results, 20 wt.% was found to be the optimum ethanol concentration for use in the SEAA process for pretreatment of corn stover.