The effects of polymerization temperature and time, initiator and monomer concentrations, ratio of water and solvent employed on the grafting of methacrylamide onto poly(ethylene terephthalate) fibers by the use of benzoyl peroxide initiator were studied. The graft yield was observed to increase with temperature and monomer concentration. The highest graft yield was obtained with an initiator concentration of 1 x 10(-2) mol/L. The rate of grafting was proportional to the power 0.48 and 1.6 of the methacrylamide and benzoyl peroxide concentrations, respectively. The overall activation energy for grafting calculated was 42.8 kcal/mol. The thermogravimetric data revealed that the thermal stability of poly(ethylene terephthalate) fibers decreased with grafting.