The enzymatic digestibility of sugarcane bagasse was greatly increased by alkali (NaOH)-peracetic acid (PAA) pretreatment under mild conditions. The effects of several factors affecting the pretreatment were investigated. It was found that when bagasse was pre-pretreated by 10% (based on initial dry materials) NaOH with 3:1 liquid-to-solid ratio at 90 degrees C for 1.5 h and further delignified by 10% peracetic acid (based on initial dry materials) at 75 degrees C for 2.5 h, the yield of reducing sugars reached 92.04% by enzymatic hydrolysis for 120 h with cellulase loading of 15 FPU/g solid. Compared with acid and alkali pretreatment, alkali-PAA pretreatment could be conducted under milder conditions and was more effective for delignification with less carbohydrates being degraded in the pretreatment process. Alkaline stage played an important role for partial delignification, swelling fibers and subsequently reducing PAA loading. No loss of cellulase activity (FPA) was observed in the liquid phase for alkali-PAA pretreated bagasse after enzymatic hydrolysis for 120 h. (C) 2008 Elsevier Inc. All rights reserved.