A numerical study of isothermal carbonization of thick wood particles has been developed. The proposed model takes into account the heat and mass transfer and chemical kinetics simultaneously. The thermal properties of wood are considered to be linear functions of the local temperature and have been estimated from literature data or by fitting the model with experimental data. The carbonization process has been described by a kinetic scheme based on a two stage semi-global kinetic model developed in a previous work of the authors. The mathematical formulation leads to a coupled nonlinear partial differential equations system, which has been solved iteratively by an implicit finite differences method. The residual mass as well as the temperature profile inside the thick particle are predicted numerically. The obtained results are in good agreement with the available experimental data. Then, the model is used to study the effect of reactor temperature and particle size on the evolution of the local temperature and mass loss inside the wood particle. (c) 2006 Elsevier Ltd. All rights reserved.