The catalytic oxidation of 4-chlorophenol (4-CP; chosen as an aromatic model pollutant) over Ni-oxide system in an aqueous medium has been studied. Experiments were carried out to investigate the effect of such parameters as pH, temperature, and catalyst dosage both on the reaction efficiency and on the reaction mechanism. The current concentrations of 4-CP as well as those of reaction intermediates-hydroquinone, benzoquinone, and 4-chlorocatechol-during the kinetic investigations were monitored by UV-Vis spectral analysis. Pseudo first-order kinetics with respect to the parent compound was observed. Experimental results demonstrated that 4-CP could be completely converted into the environmentally harmless CO2, H2O, and mineral acid under certain conditions. A probable kinetic model for the degradation pathway is proposed. (C) 2003 Elsevier Science B.V. All rights reserved.