The non-CO-involved oxidation of methanol (NCOIOM) on a Pt(111) surface is investigated by using density functional theory. Relative energy diagrams for the NCOIOM are established in which the reaction mechanisms for a catalytic cycle-including the associated barriers, the reactive energies, the intermediates, and the transient states-are shown. The results indicate that the reaction proceeds via the kinetically favored pathways: A) HCOH-->HC(OH)(2)-->HCOOH-->HCOO- [-COOH]-->CO(2) and B) CHO-->HCOOH-->HCOO- [-COOH]-->CO(2), with OH playing a key role in the entire process. The vibrational frequencies of the intermediate states derived from the calculations are in agreement with the experimental measurements.