The ozonation of two model compounds (benzenesulfonic acid and sulfanilic acid) was carried out in the presence of activated carbon. With the aim of evaluating the role of the activated carbon surface chemistry during the ozonation, two activated carbon samples were assessed. Activated carbon promoted ozonation increased the rate of removal of the selected aromatic compounds and, most of all, enhanced the removal of organic matter. Selected experiments were carried out in the presence of a radical scavenger, which evidenced the participation of HO center dot radicals in the oxidation mechanism in the degradation of benzenesulfonic acid and in the mineralization of oxidation by-products. No significant effect was observed in the degradation Of sulfanilic acid. The removal of organic carbon content from solution is due to it complex mechanism involving direct ozone reactions, adsorption and free radicals mechanisms occurring both in the liquid phase and on the activated carbon surface. Regardless of its nature, activated carbon acts both as an adsorbent of the solutes and as a catalyst in the ozonation reaction. though best results are achieved with the most basic activated carbon sample. (C) 2008 Elsevier B.V. All rights reserved.