Physicochemical analuses were performed on samples of torrefied wood obtained at various temperatures. The chemical structure of wood was strongly altered by this process ; a reactional mechanism for this is proposed in this paper. The influence of temperature and the duration of heating were compared to find the more important factors in the process. We found that these two parameters widely affected the nature oh the final product. The 3.D surfaces enabled us to predict the operating conditions which were essential to obtain a definite product with the mawimum efficiency.