Enhancement of the electrocatalytic activity of platinum for direct methanol oxidation by Ru adatoms and by the elevation of operating temperatures was investigated in hot phosphoric acid (60 to 190 degrees C). It is clear that a higher temperature operation (>100 degrees C) is advantageous for the enhancement of methanol oxidation and a maximum enhancement by Ru adatoms at each operating temperature is obtained at Pt/Ru=1/1. These results are quite similar to those obtained at low temperatures in 0.5 M H2SO4. The mechanism of the electrocatalysis on platinum electrodes with Ru adatoms in hot H3PO4 is discussed based on the experimental data in comparison with those in 0.5 M H2SO4. The rate of methanol oxidation is proportional to Ru coverage (theta(Ru)(Pt)) by the introduction of Ru sites contributing to the adsorption of oxygen species required for the oxidation of the organic species absorbed on Pt sites in a Ru coverage region of theta(Ru)(Pt)less than or equal to 0.5, but it is reduced inversely proportional to theta(Ru)(Pt) due to the reduction of a dissociative adsorption rate of methanol on the platinum sites in the region of theta(Ru)(Pt) >0.5, where the coverage of organic species becomes zero.