The graft copolymerization of styrene and acrylonitrile onto natural rubber was prepared by emulsion polymerization using potassium persulfate as an initiator. The effects of initiator concentration, reaction temperature, and pressure on monomer conversion and the grafting properties of natural rubber are investigated. A high grafting yield is obtained at a temperature of 70 degreesC, pressure of 3.1 bar, reaction time of 8 hours, and initiator concentration of 1.5 parts by weight. The copolymer composition was determined by elemental analysis. Grafted natural rubber and styrene-acrylonitrile copolymer (SAN) blends were prepared, The effect of blend composition on tensile strength, impact strength and hardness is investigated. The grafted natural rubber improves the impact toughness of SAN copolymer.