Sugarcane bagasse was treated with ultra-high pressure explosion (UHPE) in a homogenizer. UHPE significantly decreased the particle size and disrupt the microstructure of bagasse, which was changed from a rigid and highly ordered fibril to a distorted, poly-porous and "empty-inside" structure. UHPE decreased the crystallinity indexes (Crls) from 54.8% (0 MPa) to 45.3% (100 MPa), and increased the accessible surface area (ASA) of bagasse nearly 3-fold. The effect of UHPE on composition was minor, only decreased the lignin slightly. However, UHPE increased enzymatic digestibility substantially from 29.5% (0 MPa) to 59.4% (100 MPa), and the microstructure disruption and thereby ASA increase were found to be the major factors to enhance the digestibility. UHPE combination with treatment of 0.5% NaOH at 125 degrees C for 120 min exhibited a significant delignification and increased enzymatic digestibility to 95.5% with 5.8 FPU cellulase/g solid, implying that UHPE combined with alkaline pretreatment can be a potential alternative for biomass pretreatment in biofuel production. (C) 2010 Elsevier Ltd. All rights reserved.