The limiting diffusion current density in electromembrane systems is theoretically estimated by using refined Pears equation and different model approaches for the calculating of the counter-ion transport number in the membrane and its diffusion permeability differential coefficient. To this purpose, experimental data on specific conductivity, diffusion and electroosmotic permeability, as well as the apparent transport numbers of counter-ions in perfluorinated sulfocationite MF-4SK membranes with different specific water content over wide range of sodium chloride solution concentrations are used. Special features of different approaches and models used in the evaluating of the membrane parameters necessary for calculating the electrodiffusion characteristics and the limiting diffusion current are analyzed. The possibility of adequate theoretical estimation of the limiting diffusion current for ion-exchange membranes modified by organic and inorganic dopants is shown. This allows predicting the effectiveness of membranes in electromembrane processes basing on relatively simple measurements of the transport characteristics of the modified ion-exchange membranes.