Electrolytic transport processes occurring across parchment supported membranes have been described by Nernst Planck flux equation taking into account the membrane resistance R,, membrane potential E, etc. E,,, values for various electrolytes display very interesting phenomena. In the case of 1: I electrolyte the E, values are all positive, while in the case of (2: 1) and (3: 1) electrolytes surface charge reversal takes place. The diffusion rate sequence and selectivity of the membrane for different uni-bi-and trivalent cations was found to be primarily dependent on the difference in the hydration energies of counter ions in the extemai solution. On the basis of Eisenman-Sherry theory the diffusion rate sequence of alkali metal cations point towards the weak field strength of the fixed charge groups. Various thermodynamic parameters, AH', AF+ and AS* were evaluated by applying the theory of absolute reaction rates to the diffusion process through parchment supported membranes. The values of AS* were found to be negative, indicating that diffusion takes place with partial immobilization in the membrane phase. The relative partial immobility was found to increase with increase in the valence of the ions constituting the electrolyte. A formal relation between AHhydration, AFhydrslion and *Shld&" of cations with the corresponding values of AH', AF+ and AS* for diffusion, was also found to exist for these membranes.