The results are presented of investigation of electromembrane hydrolysis of cerium and lanthanum nitrates in the cathode space of a two-compartment cell with an MA-41 anion-exchange membrane and the simultaneous recovery of nitric acid in the anolyte. The phase formation of both individual and mixed nanosized (10-60 nm) cerium and lanthanum oxide products of different compositions obtained with the use of electromembrane technology and the subsequent thermal treatment has been studied. It has been shown that preliminary dehydration of the products of joint electrohydrolysis of cerium and lanthanum salts facilitates the separation of the elements by increasing the difference in solubility in dilute acids between dehydrated CeO2 and lanthanum(III) oxide compounds.