This paper deals with the oxidation of glucose in a weakly alkaline medium with platinum on carbon as catalyst. Glucose reacts very fast with chemisorbed oxygen (PtO) to yield gluconic acid, while in an oxygen-containing atmosphere a side reaction occurs, resulting in the formation of appreciable amounts of uronic acids. Most probably, this side reaction involves molecular oxygen, resulting in the oxidation of both the primary alcohol group and the aldehyde group of glucose. In the course of an experiment a strong catalyst deactivation takes place, which can be reversed by temporarily replacing the oxygen flow by a nitrogen flow. The deactivation of the catalyst is ascribed to the formation of platinum oxide (PtO2). The formation of PtO2 and the oxidation of glucose are chemically coupled. The reactivation of the catalyst in the absence of oxygen is a reduction reaction between PtO2 and adsorbed glucose.