Delignification kinetics for organosolv pulping of willow was determined using a novel method. Traditional methods of determining reaction rates and activation energy in pulping experiments involve analysis of the solid wood fraction for lignin content after pulping. This requires a large number of experimental runs to be performed to produce pulped wood having different final lignin content corresponding to different treatment time and temperature. In this paper, only four experiments are used in a reactor with a long heat LIP time and kinetic constant is determined at varying temperatures during the heat up period. This greatly reduces the number of runs required by obtaining many k values in only one run. The kinetics of organosolv delignification of hardwoods, namely Salix schwerinii, is determined and the activation energies obtained agree with previous work. (c) 2008 Elsevier B.V. All rights reserved.