Methanol oxidation effect on carbon supported Pt was investigated as a function of Pt content in a sample which is closely correlated with Pt particle sizes. After prolonged methanol oxidation the Pt particle size did not change within the experimental error ranges. The $^{13}C$ chemical shift and linewidth of CO adsorbed on Pt show non-linear behavior simply due to the Pt particle size difference. The Pt size variation difference between this work and the previous reports of the particle growths is explained by the experimental temperature difference.