Pretreatment of fibre sludge in ionic liquids and enzyme or acid catalysed hydrolysis of fibre sludge is studied. Ionic liquids, i.e. 1-allyl-3-methylimidazolium chloride ([AMIM]Cl) and 1-butyl-3-methylimidazolium chloride ([BMIM] Cl), are used in the pretreatment step. Effect of ionic liquid (IL) pretreatment on the acid and enzyme catalysed hydrolysis of fibre sludge is considered. Cellulose content of fibre sludge is more than 80 wt%, and therefore, reducing sugars obtained as a result of hydrolysis contain mostly glucose. To maximize the yield of reducing sugars during the enzymatic hydrolysis, the combinations of selective enzymes are required. Results also show that the use of ionic liquids in the pretreatment step before acid and enzyme hydrolysis increases significantly the yield of total reducing sugars. (C) 2012 Elsevier B. V. All rights reserved.