Abstract <p>A series of composite ion-exchange membranes based on the heterogeneous anion-exchange strongly basic membrane MA-41 and polyaniline was obtained via oxidative polymerization of aniline. This was achieved through sequential diffusion of an oxidizer (ammonium persulfate) and a monomer (aniline sulfate) through the membrane into water with varying contact times with the monomer solution (from 2 to 6 h). The penetration depth of the modifier into the membranes was determined to be independent of the polyaniline synthesis time and to be 30–35% of the depth of the samples. Modification of the membranes with polyaniline was found to reduce their diffusion permeability in a sulfuric acid solution of up to 20%, while increasing this characteristic in a nickel sulfate solution by 35–65% compared to the original membrane. At the same time, polyaniline modification leads to a decrease in specific conductivity, and this effect is independent of the modification duration. Asymmetry was observed in the current–voltage curves of the modified membranes, depending on the orientation of the modified surface relative to the counterion flow. Dialysis separation of sulfuric acid and nickel sulfate solutions was performed using the original MA-41 membrane and modified samples with polyaniline synthesis times of 2 and 6 h. The results showed that polyaniline influences both the acid transfer rate and the magnitude and direction of water flow during dialysis.</p>