o-Xylene combustion in air over a Pt/?-Al2O3 catalyst was investigated in a laboratory reactor at low concentrations typical for depollution applications. The results evidenced a slightly negative influence of o-xylene concentration on combustion rate. A kinetic model of the combustion process was developed by using the Langmuir-Hinshelwood mechanism, assuming the surface reaction between adsorbed oxygen atoms and adsorbed o-xylene molecules as controlling step. The rate expression includes the influences of o-xylene and water adsorption on the active centers of the catalyst. The estimation of rate expression parameters is based on o-xylene conversion measurements obtained under conditions free of influences of physical steps.