Transport phenomena in Nafion-117 perfluorosulphonic membranes have been studied by different techniques. Membrane electric conductivity has been measured under alternative current as a function of the equilibrating concentrations of MCl (M = Li, Na, K) and HCl solutions. Conductivities were found to increase for lithium and sodium membrane forms and decrease for the potassium form with an electrolyte concentration increase. The obtained data were compared with the results of diffusion permeability, ion-exchange kinetics, Li-7 and Cl-35 NMR measurements. In all cases permeability increased with electrolyte concentration growth. Diffusion coefficients and transport numbers for different counter- and co-ions were determined. The obtained data are discussed with the use of the two-phase membrane structure model. The selectivity of membrane sorption was found to increase with growth of cation radius.