The graft copolymer of xanthan gum with methacrylic acid was synthesized in inert atmosphere by using Fentos reagent as a redox initiator. The effect of reaction conditions on grafting parameters [G(%), E(%), C(%), A(%), H(%), and Rg] was investigated. Similar trend was observed on increasing the concentration of ferrous ion and hydrogen peroxide from 4.0 to 20.0 X 10(-3) Mol dm(-3) and 2.5 to 10 X 10(-3) mol dm(-3) respectively, i.e., initially grafting parameters increased and after a certain range of concentration grafting parameters showed decreasing trend. Hydrogen ion shows influenced result i.e., small increment of concentration in hydrogen ion presents much increment in percent of grafting. It was observed that the [G(%), E(%), C(%), A(%), and Rg] increased upto 6.67 x 10(-2) mol dm(-3) concentration of methacylic acid after that it decreased. Maximum G(%) was obtained at minimum concentration of xanthan gum i.e., at 40 x 10(-2) g dm(-3). The optimum temperature and time duration of reaction for maximum percentage of grafting were found to be 45 degrees C and 150 min respectively. Thermogravimetric analysis showed that the xanthan gum-g-methacrylic acid is thermally more stable than pure gum. (c) 2007 Wiley Periodicals, Inc.