In this study, a simultaneous chemical kinetics and heat transfer model is used to predict the effects of the most important physical and thermal properties (thermal conductivity, heat transfer coefficient, emissivity, reactor temperature and heat of reaction number) of the feedstock on the convective-radiant pyrolysis of biomass fuels for different geometries such as slab, cylinder and sphere. The pyrolysis rate is simulated by a kinetic scheme involving two parallel primary reactions and a third secondary reaction between volatile and gaseous products and the char. Finite difference pure implicit scheme utilizing the Tri-Diagonal Matrix Algorithm (TDMA) is employed for solving heat transfer model equation. Runge-Kutta fourth order method is used for solving the chemical kinetics model equations. Simulations are carried out for different geometries considering the equivalent radius ranging from 0.0000125 m to 0.011 m, and the temperature ranging from 303 K to 2 100 K.For conversion in the thermally thick regime (intra-particle heat transfer control), it is found that variations in the properties mainly affect the activity of primary reactions. The highest sensitivity is associated with reactor temperature and emissivity. Applications of these findings in reactor design and operation are discussed. The results obtained using the model used in the present study are in excellent agreement with many reported experimental studies, much better than the agreement with earlier models reported in the literature. (C) 2003 Elsevier Ltd. All rights reserved.