Cellulose dissolves in Bron̈sted acidic ionic liquids 1-(1-propylsulfonic)-3-methylimidazolium chloride and 1-(1-butylsulfonic)-3- methylimidazolium chloride up to 20 g/100 g ionic liquid by gentle mixing at room temperature. Hydrolysis of cellulose can be carried out in these ionic liquid solutions by the addition of 2.0 equiv of water per glucose unit of cellulose and heating the solution at 70°C and at atmospheric pressure with or without preheating to give glucose along with other reducing sugars. The hydrolysis of Sigmacell cellulose (DP ? 450) in 1-(1-propylsulfonic)-3- methylimidazolium chloride produced the highest total reducing sugar (62%) and glucose (14%) yields and was attained in 1 h of preheating at 70°C and 30 min of heating at 70°C, after adding water. © 2009 American Chemical Society.