This paper presents the studies of ethanol and acetaldehyde electrooxidation onto Pt(110) electrode modified by different osmium coverage. These oxidation reactions were studied by in situ Fourier transform infrared spectroscopy. It was shown that the catalytic activity of Pt(110) after osmium deposition for ethanol oxidation is greater than that observed on unmodified Pt(110). It was also demonstrated that the mechanistic pathway for this reaction depends directly on the degree of osmium coverage. Thus, for low osmium coverage (θ Os ≤ 0.12), the formation of CO and CO2 is not so effective when compared with other coverage degrees, and hence the full oxidation of adsorbed ethanol to CO2 is increased when the Os is deposited in the range of 0.30–0.80 ML. Additionally, the formation of acetaldehyde is also observed in low degree of osmium coverage. For a complete osmium layer (θ Os > 1.0), the catalytic activity of the electrode for ethanol oxidation shows the lowest value. The acetaldehyde oxidation reaction on Pt(110)/Os favors the CO2 production. For electrodes covered completely by Os layer, a considerable presence of CO2 above 0.8 V was observed; in contrast with the very low quantity of adsorbed COlinear, this suggests that the CO2 can also be formed from the oxidation of a possible strongly adsorbed species at high potentials on this surface, or it can also be considered that acetaldehyde can be oxidized to CO2 by the cleavage of C–C bond.