1-Allyl-pyridinium type ionic liquids with acidic anions were synthesized using a microwave-assisted method to develop a one-pot method for the direct saccharification of cellulose. A monosaccharide yield of ca. 52.4% was obtained by processing the cellulose at 100 degrees C for 1 h using a novel ionic liquid (i.e., 1-allyl-pyridinium methanesulfonate) without an additional catalyst. The first principles molecular dynamics simulations and investigations of the electronic structures of ionic liquids and cellulose revealed the mechanism of the direct saccharification of cellulose. An anion with -SO3- attracts H+ dissociated from H2O, which causes the temporary formation of the -SO3H group. Next, the -SO3H functions as an acid catalyst to hydrolyze the cellulose. In saccharification, appropriate cations, such as the 1-allyl-pyridinium cation, also play important roles. The cation interacts with the cellulose to weaken the primary chain bonds of the cellulose, which enables the decomposition of cellulose.