The effects of the potential and the pH on the electrocatalytic oxidation of glycerol at platinum electrodes were investigated by liquid chromatography during controlled potential long-term electrolyses. The selectivity towards the production of glyceraldehyde was found to depend greatly on the applied potential and on the pH of the electrolyte. In an acid medium, the dissociative oxidation of glycerol, leading to formic acid, oxalic acid and glycolic acid, is the main process observed when the potential of electrolysis is set in the so called "oxygen region" Conversely, the selectivity towards the formation of glyceraldehyde is very high when the applied potential is chosen before the beginning of the oxidation of the electrode surface. In alkaline medium, very few dissociation products were detected. However the conversion rate is sensibly increased.