A process for the work-up of a reaction mixture formed by ammoximation of a ketone, in particular an alkanone or cycloalkanone, by means of hydrogen peroxide and ammonia in homogeneous solution over a titanium-containing catalyst. It comprises the substeps removal of the catalyst, selective separation of the oxime formed in the ammoximation from the reaction mixture, removal of water of reaction and recirculation of the solvent. The work-up is carried out using at least one membrane separation step and is also successful in the case of incomplete ketone conversion and in the presence of dissolved salts.