A Pt/MgAl(O) was prepared from Pt(acac)(2) and a Mg-Al mixed oxide, synthesized from a hydrotalcite precursor, which contains extremely small Pt particles with H/Pt approximate to 1.1. Its properties were compared to that of a R/Al2O3 of a similar Pt dispersion and prepared according to exactly the same protocol. The properties of Pt were probed by H-2 and CO chemisorption followed by IR spectroscopy and microcalorimetry, and those of basic sites of Mg(Al)O by TPD of CO2. The surface basicity of Mg(Al)O decreases after deposition of Pt particles. When compared to Pt/Al2O3 a new IR absorption band of CO appears at 1960-1930 cm(-1) which was tentatively assigned to CO species bridge-bonded on Pt through the carbon atom and with Mg2+ cations by the oxygen atom. These species are most stable upon desorption at high temperature. The disproportionation of CO to adsorbed C and CO2 was occurring on Pt/Mg(Al)O. The CO2 formed migrated to basic sites of the support to form carbonates species.