Abstract The alkali-catalyzed oxidative degradation of lactose ( 1) to potassium O-β- d-galactopyranosyl-(1→3)- d-arabinonate ( 2) has been studied and compared with that of d-glucose to d-arabinonate and d-galactose to d-lyxonate. A mechanism for the degradation of 1 catalyzed by alkali only is presented and disussed, taking into consideration the main reactionproducts. Increasing the reaction temperature from 293 to 318 K resulted in a drastic decrease of the selectivity for 2. Increasing the oxygen pressure from 1 to 5 bar did not significantly influence the selectivity. The overall reaction kinetics followed first-order behavior with respect to lactose, d-glucose, or d-galactose. The simultaneous addition of catalytic, equimolar amounts of sodium 2-anthraquinonemonosulfonate and H 2O 2 showed a pronounced effect on the selectivity. A reaction mechanism for this type of alkali-catalyzed oxidative degradation of carbohydrates is presented and discussed. Lactose could be oxidized up to almost complete conversion with a selectivity of 90–95% (mol/mol), whereas d-glucose was oxidized to d-arabinonate with a selectivity of 98%. This increased selectivity was maintained at temperatures from 293 up to 323 K, allowing a reduction of the batch time necessary for almost complete conversion from 50 to 1.5 h. The overall reaction kinetics still followed first-order behavior with respect to lactose, d-glucose or d-galactose. The apparent activation energy amounted to 114 ± 2 kJ mol −1 for lactose, to 109 ± 2 kJ mol −1 for d-glucose, and to 104 ± 9 kJ mol −1 for d-galactose.