In the present article, the graft copolymer of xanthan gum with 2-acrylamido-2-methyl-1-propane sulfonic acid (AMPS) was synthesized using potassium bromate/ascorbic acid as a redox initiator in aqueous medium; reaction conditions were optimized to obtain maximum grafting ratio (%G). The optimum concentration of BrO3- ion, ascorbic acid, H+ ion, and AMPS for maximum %G were 8.0 x 10(-3), 2.8 x 10(-3), 4.0 x 10(-3), and 33.2 x 10(-3) mol dm(-3), respectively. The maximum %G (433.0) occurred at a minimum concentration of xanthan gum, i.e., 0.6 g dm(-3). The optimum time duration and temperature of the reaction for maximum % of grafting were 180 min and 45 degrees C, respectively. The graft copolymer was characterized by FTIR spectroscopy. The thermal analysis of xanthan gum and prepared graft copolymer was performed in a nitrogen atmosphere to study their thermal behavior. It was observed that the PDT (polymer decomposition temperature) of graft copolymer is lower than that of xanthan gum, whereas the IPDT (integral procedural decomposition temperature) of graft copolymer is higher than that of xanthan gum, making the former more thermally stable. The swelling and metal ion sorption capability of graft copolymer was investigated. The metal ion sorption behavior of graft copolymer was studied for five metal ions (Cu++, Ni++, Zn++, Pb++ Hg++). Our results show that the grafted sample absorbs a good amount of water and the metal ion. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 114: 1426-1434, 2009