Adsorption isotherms for thin non-uniform microporous layers are obtained in the present work with the help of the automated ellipsometry. The adsorption potential is calculated for pores of two different geometries: cylindrical and slit-like; micropore size distribution is determined using the calculated adsorption potential and the adsorption isotherms monitored by ellipsometry. Different methods of micropore size distribution calculation are analysed. It is demonstrated that the proposed calculation procedure is more informative for non-uniform microporous layers than the method proposed by Dubinin and Radushkevich. (C) 2003 Elsevier B.V. All rights reserved.