Graft copolymers of natural rubber and maleic anhydride (NR-g-MA) or maleated natural rubber (MNR) were synthesized in a toluene solution. Benzoyl peroxide (BPO) was used to initiate the free radical graft copolymerization. Influence of monomer and initiator concentrations together with effect of the reaction temperature and reaction time were investigated. Quantities of the grafted anhydride (MA) were determined by titration of the carboxylic acid functions derived from the anhydride functions. Estimation of the grafted MA level was also performed using IR absorbance ratio of the peaks at 1780-1784 cm - 1 plus 1854 cm - 1 to 835 cm - 1 . We found that quantities of the grafted MA on NR molecules increase with increasing monomer and initiator concentrations. The increase in reaction time and reaction temperature also causes increasing levels of the grafted MA. We also found that the glass transition temperature of the MNR was higher than that of the pure NR. Furthermore, the T g values increase with increasing the monomer concentration used in the graft copolymerization.