The supramolecular structure of four model celluloses was altered prior to their enzymatic saccharification using two ionic liquid pretreatments: one with the commonly used 1-ethyl-3-methylimidazolium acetate ([Emimr](+)[CH3COO](-)) and the other with the newly developed 1-ethyl-3-methylimidazolium methylphosphonate ([Emim](+)[MeO(H)PO2](-)). The estimation of crystallinity index (Crl) by solid state C-13 nuclear magnetic resonance for each untreated/pretreated celluloses was compared with the performances of their enzymatic hydrolysis. For alpha-cellulose, both pretreatments led to a significant decrease in Crl from 25% to 5% but had no effect on glucose yields. In contrast, The [Emim](+)[MeO(H)PO2](-) pretreatment on the long fibers of cellulose had no significant effect on the Crl although a conversion yield in glucose of 88% is obtained versus 32% without pretreatment. However, scanning electron microscopy analysis suggested a loss of fiber organization induced by both ionic liquid pretreatments leading to a larger accessibility by cellulases to the cellulose surface. (C) 2011 Elsevier Ltd. All rights reserved.