The effect of modification of polycrystalline platinum by Tl adatoms on the electrocatalytic properties of the electrodes towards the oxidation of monosaccharides was investigated. Significant electrocatalytic effect towards glucose and methylglucoside oxidation was observed on Pt-Tl electrodes as displayed by an enhancement of the oxidation current densities. Different carboxylic acids produced by the electrolysis of carbohydrates were analyzed by ionic chromatography. The electrooxidation of glucose on Pt-Tl gave gluconic and keto-gluconic acids, successively. When the anomeric carbon is protected (methylglucoside), the first oxidation step of the monosaccharide was carried out on the primary alcohol following the same path as that of methanol oxidation.