Highly effective cellulose solvents for the dissolution of cellulose at ambient temperature have been designed by adding any aprotic polar solvent to 1-butyl-3-methylimidazolium acetate ([C(4) mim][CH(3)COO]). The effects of molar ratio of the aprotic polar solvents to [C(4) mim][CH(3)COO], anionic structure of the ionic liquids (ILs) and nature of the co-solvents on cellulose solubility have been studied in detail. The enhanced dissolution of cellulose is suggested to be mainly resulted from the preferential solvation of cations of the ILs by the aprotic polar solvents, and this has been supported by our conductivity measurements.