A membrane which is responsive to nitrate has been developed. The membrane is nickel (Ⅱ) nitrate complex of ammonia modified Bakelite A resin which is incorporated in PVC matrix. Chemical structure of the membrane material was characterized by IR and visible spectrometry. IR and visible spectroscopic studies indicate that the amine group exists in the resin. It was also found that the nitrogens of amine groups in the membrane material are strongly coordinated to nickel(Ⅱ). Based on the chemical composition, the structure of the modified Bakelite-A-nickel(Ⅱ) nitrate complex and mechanisms for exchange with nitrate ion and for internal electrical conduction have been proposed.