A double-membrane nitrate-selective electrode [as a modified coated wire electrode (CWE)] was prepared with an internal conductor membrane made of tetrabutylammonium bromide (BrTBA) in naphthalene, and an external active membrane (Aliquat-NO 3 − in paraffin), on an Agamalgamated electrode. The nitrate-electrode exhibits linear Nernstian response over the range 1 to 10−4.5 mol/l of nitrate, with a slope of 56.01 ± 0.9 mV decade−1. The selectivity coefficients \(K_{{\text{NO}}_{\text{3}}^ - }^{{\text{Pot}}}\) for 17 ions were calculated. The effects of pH, membrane composition and thickness were also studied. The life-time of the electrode is 15 days and the stability of its potential is 0.6 mV/12 h. The electrode was preserved dry because of the better sensitivity, range of linear response and detection limit attained. The determination of nitrates in waters and fertilizers was also attemped with this electrode, using the interpolation and standard-addition methods.