A kinetic model for the ozonation of simazine in water in a laboratory bubble column is proposed. The model considers nonideal flow behavior, mass transfer, and chemical reactions; it assumes that ozone reactions develop in the slow kinetic regime of absorption; and it has been tested at different pH's and in the presence of hydrogen peroxide. The model is based on a mechanism of reactions that considers both direct and free-radical means of ozone action on simazine and some of the intermediates identified or detected. A good fit between the experimental and predicted concentrations of simazine, intermediates, and ozone in the absence of hydrogen peroxide concentrations higher than 3.4 x 10(-5) M is generally observed. For higher hydrogen peroxide concentrations, the model fails, especially, to give accurate values of the concentration of ozone in the gas leaving the column because the kinetic regime of ozone absorption changes to be moderate, a situation not accounted for by the ozone absorption rate equation applied. Comments about correcting this latter aspect are made.