A two-step acid-catalyzed hydrolysis methodology is established to effectively hydrolyze cellulose to glucose with high yield and selectivity under mild conditions. In multi-steps hydrolysis, the difficulty of cellulose can be effectively reduced under mild conditions. In the first step, microcrystalline cellulose was depolymerized in phosphoric acid to cellulose oligomer at 50 degrees C. Then the oligomer was precipitated by ethanol and hydrolyzed with dilute sulfuric acid in the second step. 87.7% total reducing sugars and 57.8% glucose was released from the two-step hydrolysis process. In addition, with the assistance of microwave in the second step, the yield and selectivity of glucose can be improved to 73.3% and 80.1% by only 5 min hydrolysis. The two-step hydrolysis exhibits an effective process to produce glucose in cellulose hydrolysis. The enhancement of hydrolysis reactivity is considered to be controlled with the decrease of crystallinity and degree of depolymerization of cellulose. (C) 2013 Elsevier Ltd. All rights reserved.