Some kinetic features of the grafting of methyl methacrylate onto polyethylene terephthalate initiated by the potassium bromate-thiourea redox system have been investigated in aqueous solution. The effects of potassium bromate, thiourea, monomer, acid, and temperature upon percentage grafting have been determined. The activation energy of the reaction has been computed from an Arrhenius plot. Grafting experiments have been carried out in the presence of such conventional chain-transfer agents as CC14and CHC13. The effect of CuSO4upon grafting is also studied. The reaction mechanism involved during grafting is pictured.