In view of decreasing the amount of IL to achieve efficient simultaneous pretreatment and saccha-rification, a comprehensive study was undertaken. Different types of lignocellulosic biomasses were investigated in various enzymatic aqueous-IL systems including 1-ethyl-3-methylimidazolium acetate ([C2mim][OAc]) or 1-ethyl-3-methylimidazolium methylphosphonate ([C2mim][MeO(H)PO2]). To better understand how 10% (v/v) of IL in the reaction medium led to the highest yields of glucose without fractionation from sawdust, distinct cellulosic models were then used as substrates. Kinetic studies demonstrated that both ILs affect synergistic action of cellulolytic enzymes depending on both consti-tutive anion and cellulosic substrate. Concentrations above 10% v/v of ILs deactivated cellulase even on highly digestible model substrates. and Kamlet-Taft parameters constituted more physicochemical pertinent indicators than apparent pH value to investigate effects of IL on cellulase performances. Fine description of these effects was proposed onto individual EG, CBH and BG. [C2mim][MeO(H)PO 2 ] was demonstrated a better compatible IL for enzymes up to a concentration of 30% (v/v). The efficiency of simultaneous pretreatment and saccharification was governed by a compromise between better substrate accessibility and enzyme deactivation.