The graft copolymerization of methyl methacrylate(MMA) onto natural rubber latex(NRL) initiated by t-butyl hydroperoxide(t-BHPO) was investigated in aquous medium. The grafting percentage, grafting efficiency and total conversion were observed in various reaction conditions such as monomer, initiator and emulsifier concentration, reaction temperature, reaction time and agitation speed. The optimum conditions for the graft copolymerization onto natural rubber latex were as follows ; At given monomer concentration of $3{ imes}10^{-2}mole/l$, the maximum grafting percentage was appeared in the case of grading in initiator concentration of $4{ imes}10^{-2}mo1e/l$ and emulsifier concentration of 0.2wt.% at $40^{circ}C$ for 5hrs.