Simultaneous IL-pretreatment and enzymatic saccharification of biomasses succeeded. 10% v/v of IL led to highest yields of saccharification without fractionation. [C2mim][MeO(H)PO2] was more powerful than [C2mim][OAc] for one-step process. Synergistic action of cellulases in IL-aqueous media was influenced. A compromise between substrate accessibility and enzyme deactivation governed.