IrO2+SnO2 mixed oxide electrodes were prepared by thermal decomposition at 400degreesC over the whole composition range. Data of XPS and cyclic voltammetry (CV) have shown considerable surface enrichment with IrO2. Consistently, O-2 evolution from acid solution (H2SO4), for precious metal oxide contents > 10%, proceeds with kinetic parameters close to those of pure IrO2. The Tafel slope, IR-drop, reaction order (H+ and surface sites), electrocatalytic activity and stability have been scrutinized as functions of active layer composition. A reaction mechanism has been proposed. For some of the compositions the effect of the solution temperature was also investigated. The kinetics of O-2 evolution appear to conform to the 'standard' Butler-Volmer model. IrO2+SnO2 electrodes were found to be stable under O-2 evolution within the time scale of the present work.