The combined application of chemical techniques and HREM shows that platinum deactivation in Pt/CeO2 catalysts steadily increases with the reduction temperature (T-r : 473-1173 K). Though no suppression of the H-2 adsorption was observed, the TPD-H-2 traces indicate the occurrence of significant chemical changes with T-r. As revealed by HREM, the metal decoration starts at T-r : 973 K, a temperature well above those at which the chemical effects can be observed.