A process for converting lactose into carbon dioxide and/or carbon monoxide using catalytic wet oxidation. Oxygen gas and an aqueous solution of lactose are fed to a reactor comprising a Pt/Al.sub.2O.sub.3 catalyst, a Mn/Ce catalyst or a Pt/Mn--Ce catalyst, and the lactose is oxidized in the reactor at elevated temperature and pressure to produce at least one of small organic acids, carbon dioxide, carbon monoxide, water and combinations thereof. The small organic acids may be further degraded by feeding the small organic acids and oxygen gas into a reactor containing a Mn/Ce catalyst and oxidizing the small organic acids to water and at least one of carbon dioxide, carbon monoxide and combinations thereof.