Abstract The pore structure of heterogeneous ion exchange membranes was studied by the mercury penetration method using a commercially available apparatus. Results obtained from the porosymmetrical measurements show that the membranes possess two layers, the upper one being less porous than the lower backing layer. The distribution of the pores in width and length is non-homogeneous. Anion exchange membrane MA-41 has a relatively more homogeneous pore structure. Application of the mercury penetration method makes it possible to quantitatively assess the degree of mechanical destruction of anion exchange membranes during the working period. It was found that membranes operated at the cathode and anode compartments of the electrodialysis unit are destroyed more quickly.