A new kinetic model for heterogeneous photocatalytic reactions has been developed as an alternative to the Langmuir-Hinshelwood (L-H) and the Direct-Indirect (D-I) models. The L-H model has been widely used to analyze the kinetics of the TiO2-photocatalytic degradation of water-dissolved organic compounds, assuming the adsorption/desorption equilibrium of the reactants (Langmuir isotherm). Nevertheless, it has been reported by some authors that the experimental data on photocatalytic oxidations are incompatible with the behavior predicted by L-H model. The proposed model, unlike the L-H model, considers all the basic steps involved in heterogeneous photocatalysis with TiO2, including the back reaction involved in the process, and it is applicable to organic species non-adsorbed on the TiO2 surface. In the case of phenol photodegradation, the proposed model better describes, mechanistically, the experimental data than L-H and D-I models. (C) 2011 Elsevier B.V. All rights reserved.