The TiO2-assisted photocatalytic degradation of gas-phase dimethyl sulfide (DMS) is studied. Catalyst activity deactivation due to consecutive experiments carried out with the same catalyst sample is characterized. Changes in kinetics behavior and reaction rate constants are attributed to the change of the number of available active sites that takes place during catalyst deactivation. Detection of surface and gas-phase reaction intermediates and final products is done in an attempt to relate their contribution to the deactivation phenomena. A reaction mechanism is suggested based on both, intermediates found in this study and previous mechanisms reported by other authors for the gas-phase heterogeneous photocatalytic degradation of similar S containing compounds. Recovery of the surface activity with soft gas-phase treatments was unsuccessful indicating the irreversible nature of the deactivation. (C) 2004 Elsevier B.V. All rights reserved.