Deproteinized natural rubber (DPNR) latex was prepared by the incubation of fresh natural latex with a proteolytic enzyme. The DPNR latex was later used to prepare a graft copolymer with methyl methacrylate (MMA). High ammonia (HA) concentrated latex was also used to prepare a graft copolymer with MMA. The appropriate reaction time was 3 h at a reaction temperature of 50degreesC. The conversion percentage of the graft reaction with DPNR was higher than that of the system with HA. The grafting efficiency percentage decreased with an increasing concentration of MMA in the graft reaction. In a comparison of the two types of latices, it was found that the reaction with DPNR provided higher grafting efficiency. Furthermore, a larger quantity of grafted poly(methyl methacrylate), a larger average particle size, and fewer free natural rubber molecules were also observed in the grafting system with DPNR. The difference between the reactions of the DPNR and HA latices was attributed to the removal of proteins, which acted as free-radical scavengers. They terminated the free-radical species during the graft copolymerization.