A novel type of weakly acidic cation exchange fiber (SC-IEF) was prepared by oxidizing the semi-carbonized polyacrylonitrile fiber (SC-PAN) with nitric acid solution. The physicochemical properties and adsorption performance of SC-IEF were characterized. Effects of the temperature, reaction time, concentration and dosage of nitric acid on the oxidation process of SC-PAN were studied. The experimental results indicate that the SC-IEF prepared shows higher thermal stability than conventional ion exchange fiber based on the hydrolysis of polyacrylonitrile. The content of the surface oxygen-containing groups on SC-IEF is up to 3.78 mmol/g. The static adsorption capacities of SC-IEF for Pb2+, Cu2+ and Mg2+ ions are 25.4. 8.2 and 4.5 mg/g, respectively, which reveals an excellent adsorption property of this novel ion exchange fiber. SC-IEF also shows an excellent selectivity for the adsorption of Pb2+ ions with the coexistence Of Cu2+ and Mg2+ ions in the solution. (C) 2008 Elsevier Ltd. All rights reserved.