Pretreatment of rice straw by steam explosion prior to enzymatic saccharification has been investigated. The study sought the optimum conditions of steam pressure and steaming time. Rice straw was exploded at various steam pressures (2.55, 3.03, 3.53 and 4.02 MPa) for steaming times ranging front 0.5 to 10 min. The susceptibility of the pretreated substrate to cellulase enzymes was greatly influenced by the steam pressure and steaming time of pretreatment. It was found that high steam pressure (3.53 MPa) for a short steaming time (2 min) effectively enhanced enzymatic saccharification and alcohol fermentation of rice straw The results demonstrated that no additional treatment, such as extraction with water or chemicals, is required to hydrolyze the steam-exploded sample to a greater extent if it is pretreated under an optimized set of conditions. Copyright (C) 1996 Elsevier Science Ltd.