Lignocellulosic biomass as a sustainable source of biofuels and value-added renewable materials is hindered by the high processing costs and relative low sugar yields. Switchgrass is of great interest as a potential bioenergy feedstock. A new cellulose-solvent-based lignocellulose fractionation (CSLF) technology has been developed for separating lignocellulose components based on their different solubility in different solvents under modest reaction conditions (Zhang et al. Biotechnol. Bioeng. 2007. 97: 214). This technology is regarded as a nearly generic pretreatment addressing different types of feedstock with the high enzymatic glucan digestibility within a short reaction time. The optimal pretreatment conditions for switchgrass were determined to be 85% H₃PO₄ at 50^oC for 45 minutes. A 3-fold reduction in total enzyme loadings from 15 FPU of cellulase and 30 CBU of ß-glucosidase per gram of glucan to 5 FPU of cellulase and 10 CBU of ß-glucosidase per gram of glucan still lead to ~90% glucan digestibility within 24 hour hydrolysis. Scanning electron microscopy (SEM) images clearly show that CSLF can completely destruct fibril structure of recalcitrant lignocellulosic biomass. Quantitative surface area data show that CSLF can break lignocellulosic structure efficiently, resulting in a very high surface area of cellulose fraction and a decrease in the degree of crystallinity. Therefore, the pretreated switchgrass by CSLF possesses high enzyme hydrolysis rates and high sugar yields.