The ion association complex of is(neocuproine)-copper(I) and nitrate has been employed as new electroactive material for a nitrate ionselective electrode. Two different types of the electrode constructions have been examined, liquid-state electrode and PVC plastic membrane electrode with direct solid contact. Data on sensitivity and selectivity of these systems are reported. The PVC membrane electrode has been employed for the potentiometric nitrate determination in tap water (>0.2ppm of NO3−-N).