Abstract: This article investigates the transformation processes of dehydro-L-ascorbic acid on commercial Granucol GE activated carbon when heat treated in air at a temperature of 350°C. It has been established that vitamin C (L-ascorbic acid) on coal is oxidized to dehydro-L-ascorbic acid before heating. It has been shown that dehydro-L-ascorbic acid decomposes with the formation of compounds with alcohol, carboxyl and carbonyl groups and the release of CO₂ upon heating for 40 min. After regeneration, the sorption capacity of the coal decreases to 86.8%. The data obtained from the isotherms of N₂ adsorption show that the specific surface area and the pore volume of the regenerated coal are lower than those of the pure coal. Dehydro-L-ascorbic acid molecules protect to some extent the active centers of the coal during heat treatment. A scheme of the processes of thermal degradation of dehydro-L-ascorbic acid on coal surface is proposed.