Corn stover is one of the most common lignocellulosic biomass used in bioethanol production. In bioethanol production, pretreatment is the first step to break down recalcitrant structure of biomass which is also a critical process for further sugar release and fermentation. Among all chemical pretreatment processes, ammonia is one of the base reagent, and the low moisture anhydrous ammonia (LMAA) process could minimize water and ammonia input in bioethanol production. For obtaining the optimal fermentable sugar yields with the most efficient chemical loadings and pretreating time, several factors were examined for enzymatic digestibility optimization. In LMAA pretreatment process, the ammonia loading, ammoniation time and the particle size of corn stover are the main factors for enzyme digestibility in the hydrolysis process. As the particle size of corn stover was reduced from 1mm to 0.5 mm, the anhydrous ammonia loading was increased from 0.1g to 0.18g NH₃/g DM biomass under 75^oC and the ammoniation incubation was extended from 72 hr to 144 hr, the enzyme digestibility would increase from 71.6% to 83.69% with about 17% increments.