Abstract: Tailoring of new thickener via graft copolymerization of methacrylonitrile (MAN) onto pregelled starch (PGS) as a carbohydrate polymer was synthesized and the reaction conditions were optimized using potassium monopersulphate (PMPS) in presence of ferrous ion redox pair as initiator. Emphasis was directed towards preparing new thickener for printing cotton fabrics with reactive dyes. The grafting parameter was studied with respect to Graft Yield (GY) and Graft Reaction Efficiency Percent (GRE%). On the other hand, the newly prepared poly (MAN)-pregelled starch graft copolymers were used as a thickener for printing cotton fabrics with reactive dyes, to see their suitability as pastes for printing cotton with the latter dyes. Based on the results obtained, appropriate conditions for grafting methacrylonitrile onto pregelled starch was established and the graft yield is higher under the following conditions: using 0.004 mol L-1 potassium monopersulphate as initiator, 0.005 mol L-1 ferrous ion concentration, 0.002 mol L-1, sulphuric acid; 50% methacrylonitrile concentration (based on weight of substrate), material to liquor ratio, 1:2.5, reaction time, 60 min and polymerization temperature, 40 °C. Finally, utilization of poly (MAN)-pregelled starch graft copolymers as a new thickener for printing cotton with reactive dyes proved to be a potential thickener as evidenced by excellent color strength as well as overall fastness properties.