This article reports the synthesis, characterization, and ion exchange properties of a terpolymer. The terpolymer resin salicylic acid-diaminonaphthalein-formaldehyde (SDNF) was synthesized by the condensation of salicylic acid and diaminonaphthalein with formaldehyde in the presence of a hydrochloric acid catalyst. Terpolymer resin was characterized by elemental analysis, infrared (IR) spectroscopy, nuclear magnetic resonance spectroscopy, and UV Visible spectral studies. The number average molecular weight of the resin was determined by nonaqueous conductometric titration. Chelation ion exchange properties have also been studied for Fe3+, Cu2+, Co2+, Zn2+, Cd2+, Pb2+ ions employing a batch equilibrium method. It was employed to study the selectivity of metal ion uptake involving the measurements of distribution of a given metal ion between the polymer sample and a solution containing the metal ion. The study was carried out over wide pH range and in a media of various ionic strengths. The terpolymer showed higher selectivity for Fe3+, Cu2+, and Ni(2+)ions than for Co2+, Zn2+, Cd2+, and Pb2+ ions. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 117: 315-321, 2010