The kinetics of pyrolysis of rice husk was studied under non-isothermal heating in air or nitrogen media. Based on TG curves, the kinetic parameters of the process were calculated using the method of Coats-Redfern and fourteen kinetic equations. It was found that the experimental data were best described by the equation of Ginstling-Brounshtein valid for diffusion-controlled reactions starting, on the exterior of spherical particles with uniform radius. The values of activation energy, frequency factor, change of entropy, enthalpy and Gibbs energy were calculated for the formation of the active complex of the reagent. The diffusion control of the pyrolysis process was explained with the high strength of the Si-O carcass of the biomass which impeded the release of volatile products. It was confirmed also by the similarity of the kinetic curves and electron microscopy photographs of the hard residue obtained after pyrolysis in oxidative or inert medium. (C) 2003 Elsevier B.V. All rights reserved.