MgO pretreatment was investigated to boost the fermentable sugars derived from corn stover with LHW pretreatment as control. Compared to LHW pretreatment, MgO pretreatment caused twice hemicellulose recovery (42 vs 21%). Double hemicellulose recovery not only didn't affect glucose yield but increased xylose yield by 13% and total sugar yield by 6% under the optimal conditions (pretreatment: 10% biomass loading, 0.1 mol/L MgO, 190 degrees C, and 40 min; hydrolysis: pretreated biomass loading of 10 g/100 mL, enzyme loading of 1 mL/g pretreated biomass, 50 degrees C, and 120 h). A total sugar concentration of 50 g/L was obtained under the above conditions. Besides, the enzyme component hydrolyzing xylan may be prone to deactivation by lignin residues in pretreated biomass. Both SEM and FTIR analyses indicate that MgO effectively disrupted the biomass structures and enlarged the exposed surface area of carbohydrates, thus boosting the enzymatic hydrolysis and fermentable sugars for ethanol production.