New thermoplastic soy protein isolated (SPI) and methyl acrylate (MA) copolymers (T-SPI-g-MA) were prepared using graft copolymerization and initiated with ammonium persulfate (APS). The reaction conditions such as initiator concentration and temperature on the graft percentage (GP) were investigated. The single factor experimental showed that the optimal conditions for grafting of 15g SPI were: 4 g initiator of APS, 60 mL monomer of MA and in 250 mL 2M urea aqueous solution at 70 °C for 3 hours. The products were characterized by means of FT-IR and DSC. The results indicated that the monomer was grafted successfully on SPI and the T-SPI-g-MA had a glass transition at 22 °C.