An active coating, composed of a mixture of nanocrystals of RuO2 with the rutile structure and nanocrystals of metal Pt, was thermally synthetized on a titanium substrate. Cyclic voltammograms and polarization curves showed that the catalytic activity of the coating for the formic acid oxidation in an acidic solution increased with an increase in the RuO2 content, reaching the maximum value at 50 mol % RuO2. Additionally, further increase in the RuO2 content resulted in a decline of the catalytic activity. The catalytic effect was attributed to a bifunctional mechanism and an electronic effect. The bifunctional mechanism had a dominant role and was based on the fact that Ru–OH species were formed on Ru atoms of RuO2 at more negative potentials than on Pt. Those species oxidized the adsorbed COad and HCOOad—species on adjacent Pt atoms of clusters of metal Pt and thus discharge them to oxidize new HCOOH molecules.