The effects of several critical factors including H2O/cellulose molar ratios, dissolution temperatures (T-dis), dissolution times (t(dis)), reaction temperatures (T-rxn), reaction times (t(rxn)), and types of ionic liquids (IL) were investigated for cellulosic conversion. We optimized the reaction conditions as: H2O/cellulose = 10/1, T-dis = 120 degrees C, t(dis) = 0.5 h, T-rxn = 120 degrees C, t(rxn) = 3 h for 1-ethyl-3-methylimidazolium chloride ([EMIM]Cl)-based system, and the maximum yield of 5-hydroxymethylfurfural (HMF) up to 21% could be achieved without adding extra catalysts. Another pyridinium-typed IL, [Epyr]Cl, was also used in the cellulosic conversion, and the results showed a high selectivity toward monosaccharides. The information obtained in this study will benefit many biofuel-related applications. (C) 2011 Elsevier B.V. All rights reserved.