A xanthan gum-g-N-vinyl formamide graft copolymer was synthesized through the graft copolymerization of N-vinyl formamide (NVF) onto xanthan gum with an efficient system, that is, potassium monopersulfate (PMS)/Ag(I) in an aqueous medium. The effects of the concentrations of Ag(I), PMS (KHSO5), hydrogen ion, xanthan gum, and NVF along with the time and temperature on the graft copolymerization were studied by the determination of the grafting parameters (grafting ratio, add-on, conversion, grafting efficiency, and homopolymer) and the rate of grafting. The maximum grafting ratio was obtained at a 0.6 g/dm(3) concentration of xanthan gum. All the parameters showed an increasing trend with an increasing concentration of peroxymonosulfate, except the homopolymer percentage, which showed a decreasing trend. The grafting ratio, add-on conversion, grafting efficiency, and rate of grafting increased with the concentration of Ag(I) increasing from 0.8 X 10(-2) to 1.2 X 10(-2) mol/dm(3). The optimum time and temperature for the maximum degree of grafting were 90 min and 35 degrees C, respectively. The graft copolymer was characterized with IR spectral analysis, thermogravimetric analysis, and differential calorimetry analysis. (c) 2006 Wiley Periodicals, Inc.