The additive cation effect on the oxidation-resistance of platinum supported on alumina was investigated by Pt L-III and L-II-edge XAFS. The white line intensity at Pt L-III-edge of oxidized catalysts decreased with an increase in the electronegativity of the additive cation in the same way as the support effect previously reported: The addition of electrophilic cations make the supported platinum less oxidized state compared with the original Pt/Al2O3 and vice versa. Thus, it was revealed that the addition of more electrophilic cations provides the higher oxidation-resistance to platinum catalyst, even when platinum is supported on basic oxides.