Graft copolymer of glycidyl methacrylate and styrene onto natural was synthesized by emulsion polymerization using cumene hydroperoxide and tetraethylene pentamine as a redox initiator. The effects of initiator and monomer conversion were investigated. The grafted natural rubber was characterized by FT-IR spectroscopy and NMR analysis. Dynamic mechanical properties and morphology of grafted natural rubber to be at the monomer concentration of 100 phr, the initiator concentration of 2.5 phr and temperature of 60℃ for 10 hours. The grafted natural rubber product could be used as a compatibilizer for STR5L/PMMA blends. The mechanical properties such as tensile strength, elongation at break, tear strength, hardness and impact energy were evaluated as a function of grafted natural rubber content. The good mechanical properties of unvulcanized and vulcanized of STR5L/PMMA blends were obtained at 5-10 phr of grafted natural rubber content. The mechanical properties of grafted natural rubber/PMMA blends were also studied. The tensile strength, tear strength and hardness increased with increasing of PMMA content. The tensile fracture surface examined by scanning electron microscopy between the two phases of blend.