A new type of an ion selective electrode for nitrate ion was developed. Silver diethyldithiocarbamate, obtained by mixing a silver nitrate solution to a sodium diethyldithiocarbamate solution, was used as the active membrane material. The response to nitrate ion is linear with a Nernstian slope (60 mV/1 pNO3) over the concentration range 10−1to 10−6M in the pH range from 4 to 11. From IR spectra, the potential response to nitrate ion may arise from nitrate ion adsorbed in the membrane material. No response is observed to any cations, except hydrogen, mercury (II) and silver ions.