Abstract Samples of platinum crystallites finely dispersed on silica and silica–alumina were prepared by impregnating a series of SiO 2–Al 2O 3supports with aqueous PtCl 4solutions. Reduced platinum samples were oxidized by dioxygen to examine variations of platinum-oxides (Pt-O x ) species formed with the oxidation temperature ( T O). Both PtO and PtO 2species were verified to coexist on oxidized Pt/SiO 2samples according to characterizations by techniques of X-ray photoelectron spectroscopy and temperature-programmed reduction (TPR). TPR spectra of oxidized platinum species dispersed on SiO 2–Al 2O 3supports exhibited six peaks of different reduction temperatures ( T r). These peaks were assigned to PtO and PtO 2species dispersed in silica-rich grains ( T r=−40 and 20°C, respectively), in alumina-rich grains ( T r=50 and 90°C), and in pores of the grain boundary ( T r=110 and 130°C), respectively. The contribution of these six species varied with both the temperature of oxidation treatments and the Al 2O 3/SiO 2ratio of sample supports.