A kinetic model of peracetic acid brightening of a solvent-assisted ozone delignified pulp was developed. The model consists of three parallel and one consecutive reaction, and is based on reaction pathways reported for lignin model compounds with peracetic acid. An optimization search algorithm was used to find the kinetic parameters of the model. The kinetic model provides an adequate description of the disappearance rate of the chromophores in pulp at constant pH and peracetic acid concentration.