AbstractTransport processes in the systems sulfonic acid membranes (NAFION‐120 or MRF‐26)/sulfuric acid solutions are discussed applying non‐equilibrium thermodynamic approach.For this purpose the phenomenological resistance and friction as well as coupling coefficients were calculated. The coefficients were extended to all the components, i.e. hydrogen ions, sulfuric acid anions, water, and polymer network.As the most important feature determining transport phenomena, the interaction between anions and the polymer network, having a maximum at the same relative concentration of sorbed acid to that of fixed charges in both membranes, was recognized.The second factor is the specificity of hydrogen ions, resulting in a small interaction of those ions with the polymer network, as well as essential coupling of large hydrogen ions and water st