The optimum conditions for grafting N-vinyl-2-pyrrolidone onto dextran initiated by a peroxydiphosphate/thiourearedox system were determined through the variation of the concentrations of N-vinyl-2-pyrrolidone, hydrogen ion, potassium peroxydiphosphate, thiourea, and dextran along with the time and temperature. The grafting ratio increased as the concentration of N-vinyl-2-pyrrolidone increased and reached the maximum value at 24 x 10(-2) mol/dm(3). Similarly, when the concentration of hydrogen ion increased, the gafting parameters increased from 3 x 10(3) to 5 x 10 mol/dm(3) and attained the maximum value at 5 x 10(-3) mol/dm(3). The grafting ratio, add-on, and efficiency increased continuously with the concentration of peroxydiphosphate increasing from 0.8 x 10(-2) to 2.4 x 10(-2) mol/dm(3). When the concentration of thiourea increased from 0.4 x 10(-2) to 2.0 x 10(-2) mol/dm(3), the grafting ratio attained the maximum value at 1.2 x 10(-2) mol/dm(3). The grafting parameters decreased continuously as the concentration of dextran increased from 0.6 to 1.4 g/dm(3). An attempt was made to study some physicochemical properties in terms of metal-ion sorption, swelling, and flocculation. Dextrang-N-vinyl-2-pyrrolidone was characterized with infrared spectroscopy and thermogravimetric analysis. (C) 2008 Wiley Periodicals, Inc. J Appl Polym Sci 110: 3455-3463, 2008