Electrochemical impedance spectroscopy (EIS) was applied to study charge transfer and ion diffusion processes of all-solid-state ion-sensitive electrodes based on zeolite-polydimethylsiloxane (PDMS) membranes. In order to investigate the effects of zeolites embedded into a polymer matrix membranes with different types and contents of zeolites were characterised. On the basis of EIS studies, zeolites of the faujasite type were found most suitable for potentiometric determinations. This result can be attributed to the large pore size of 7.4 Angstrom and a low Si/Al ratio. The differences in selectivity of potentiometric responses towards alkali metal cations and tetrabutylammonium cations were found to be reflected by differences in the bulk resistance of the membrane. The impedance behaviour of the zeolite-polymer electrodes was modelled by an appropriate equivalent electrical circuit.