The conducting polymer poly(3,4,-ethylenedioxythiophene), PEDOT, doped with multi-walled carbon nanotubes and fullerenes, C(60), were used as the ion-to-electron transducing layers in all-solid-state potassium selective electrodes. The electrochemical properties of the transducing layers were studied by cyclic voltammetry and electrochemical impedance spectroscopy. Electrodes with both solid contacts showed good linear potentiometric response with almost Nernstian slope. Purging the solution with oxygen and carbon dioxide did not affect the potential stability of the electrode with the conducting polymer transducing layer. Selectivity of the electrode with the fullerene solid contact is comparable with conventional K(+) selective electrodes. Electrodes with both type of solid contacts showed good long term potential stability.