The electro-oxidation of l-ascorbic acid is examined on three low index planes of gold single crystals in various aqueous electrolytes. The overall oxidation process in the double-layer potential region of gold consists of two major stages. The first stage is structure insensitive and is not affected significantly by anions of different specific adsorption ability. This stage corresponds to an outer-sphere two-electron transfer process with the formation of dehydro-l-ascorbic acid and/or its hydration product as the primary product. The second stage is structure sensitive and is affected significantly by the anions in solution. This stage is believed to correspond to the further oxidation of dehydro-l-ascorbic acid, which is an inner-sphere process.