Several thallium(I) ion-selective electrodes based on quinoline-carbonitrile compounds as a novel class of sensors have been prepared and studied. The optimum thallium(I) ion-selective electrode is made from 2-cyclohexylthio-4-oxo-1(4H)quinoline-3-carbontrile as the electroactive material.This electrode exhibits a Nernstian response for 0.1-1.0 x 10(-5) M TINO3 with a slope of 56 mV decade(-1). The detection limit is 3.2 x 10(-6) M. The electrode shows a high selectivity, stability and reproducibility and can be used as a sensor in potentiometry.