Acrylonitrile was successfully grafted on polystyrene modified with activated carbon using gammairradiation technique. This process was carried out modified at various gamma dose (0.2 to 1.5 Mrad). The new grafted polymer (GP) was characterized and its properties were investigated. In this study, it was found that 2 gm of polystyrene, 90% (w/w) acrylonitrile monomer, 2% (w/w) ferrous ammonium sulfate (FAS) catalyst, 1 mg activated carbon powder and 1.25 Mrad gamma dose are the optimized conditions required for the polymerization of GP. The grafted polymer was proved by Fourier transform infrared (FTIR), thermo gravimetric analysis (TGA) and UV-visible spectroscopy. A mechanism is presented to explain the formation of GP.