The performance characteristics of a copper (II) ion-selective electrode, based on pressed-pellet membrane of ternary CuAgSe, are reported. The sensing material is isostructural with the natural mineralβ-eucairite and shows high corrosion resistivity which results in stable and reproducible electrode performance upon ageing. The electrodes exhibit a linear Nernstian response dawn to 5.10−8M in non buffered medium and down to 10−13M in copper-glycine ion buffer. Data on the electrode stability for a period of two and a half years, on the electrode response time, pH-dependence, selectivity etc. are also presented.