A plasticized ion-selective membrane based on PVC matrix which tricrezylphosphate (TCP) and containing K+ - ionophores (dibenzo-18-crown-6 and decyl-18-crown-6) was used to obtain a potentiometric potassium sensor. The potassium selective membranes were characterized in terms of their electrochemical and physical properties, surface morphology and structural parameters. The a.c. impedance, UV/VIS analysis of the membranes was also studied.