Polysaccharide based graft copolymer (xanthan gum-g-4-vinyl pyridine) was synthesized using potassium peroxymonosulphate/ascorbic acid redox initiator in inert atmosphere at 40 degrees C. By studying the effect of the concentration of monomer, peroxymonosulphate (PMS), ascorbic acid (AA), xanthan gum (XOH), hydrogen ion along with effect of time and temperature on grafting characteristics: grafting ratio (%G), add on (%A), conversion (%C), efficiency (%E), homopolymer (%H), and rate of grafting (Rg), the reaction conditions for optimum grafting were determined. The optimum concentration of AA, H+ ion, 4-VP for maximum grafting were found to be 10.0 x 10(-3) mol dm(-3), 2.5 x 10(-2) mol dm(-3), 10.0 x 10(-3) mol dm(-3), respectively. Maximum %G was obtained at minimum concentration of xanthan gum i.e., at 40.0 x 10(-2) g dm(-3) and at maximum concentration of PMS i.e., at 10.0 x 10(-3) mol dm(-3). The optimum temperature and time duration of reaction for maximum % of grafting were found to be 45 degrees C and 120 min respectively. The synthesized graft copolymer was characterized by FTIR analysis. Thermogravimetric analysis showed that the xanthan gum-g-4-vinyl pyridine is thermally more stable than pure gum. A probable mechanism Was Suggested for the graft copolymerization. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 112: 1407-1415, 2009