Within the frame adsorbents production from biomass. this study proposes to investigate the change in pore size distribution during the pyrolysis. The mercury intrusion method has been used to measure pore structure and a mathematical model has been developed based on the population balance and the mass balance. This model considers particle shrinkage, different kinds of new pore initiation, and the coalescence of pores. These different kinds of pore size contributions are presented starting from the measured pore size distribution of larch wood. (C) 2002 Published by Elsevier Science B.V.