As discussed above, a large amount of hemicelluloses and lignin were removed from the biomass to the spent liquor during the pretreatment process. An important point that must be considered is regarding the changes of their existing forms in hydrolysates. Especially some of compounds derived from the sugar degradation had been known as potential inhibitors for subsequent fermentation (Palmqvist and Hahn-Hägerdal, 2000). Considering that the formation of these compounds was closely correlated with pretreatment conditions, the amount of several known fermentation inhibitors and soluble sugars in spent liquor were listed in Table 1 as a standard to evaluate the degradation of three key components during MBSP process.