Biomass and waste are recognized to be major potential sources for energy production. Gasification enables the conversion of these materials into combustible gas, mechanical and electrical power, synthetic fuels and chemicals. In view of the considerable interest in the gasification process worldwide, it is necessary to model and predict the performance of the gasifier in priori. Modeling of biomass gasification implies the representation of chemical and physical phenomena constituting pyrolysis, combustion, reduction and drying in a mathematical form. In the present study, steady state composition and temperature profiles for the reduction zone of a downdraft biomass gasifier are predicted. A model reported in the literature is modified by incorporating the variation of the char reactivity factor (CRF) along the reduction zone of the downdraft biomass gasifier. Increasing the CRF exponentially along the reduction bed length in the model gave better predictions of the temperature and composition profiles when compared with the experimental data and earlier models reported in the literature. (c) 2005 Elsevier Ltd. All rights reserved.