Among a series of Pt-supported catalysts prepared by impregnation, the most hydrophobic Pt-supported on MCM-41 (synthesized in the presence of fluoride anions) with large surface area and pore size is found to be the most active catalyst for the combustion of toluene in air, and its activity is maintained even in the presence of water. However, Pt/ZSM-5 with micropores, the smallest pore volume and the least hydrophobicity has the worst catalytic activity. The high oxidation activity of the catalyst depends mainly on its high hydrophobicity (characterized by selective adsorption for H2O and toluene and by FTIR spectra of surface hydroxyl groups) and partly on its large pore size and high Pt loading. The order of the oxidation activity of a series of aromatics with different molecular weight and different boiling point on Pt-supported MCM-41 catalyst is found to be as follows: toluene > benzene > cumene > ethyl benzene > mesitylene.