Lactose oxidation to lactobionic acid was investigated over palladium forms of Beta and MCM-22 zeolites. Different support acidity and the method of palladium introduction were applied. It was observed that the catalyst preparation methods, as well as acidity, influence the activity and selectivity. Pd-H-MCM-22 zeolites were more active, than palladium on conventional supports, for instance silica and alumina, or beta zeolite. In situ catalyst electrochemical potential measurements were applied as a source of supplementary information to monitor the coverage of adsorbed species, in particular oxygen, during the reaction.