In this study the grafting of acrylamide-methacrylic acîd monomer mixture upon poıy (ethylene terephthalate) fibers using benzoyî peroxide as initiator was investigated. The increase of benzoyl peroxide concentration above 0.0968 g/50 mİ decreased the graft yield. The vari- ation of the graft yield with temperature was also investigated in the range of 65-92 ÛC. Maxi- mum graft yield was obtained at a acrylamide-methacrylic acid mixture ratio of 50 /50 (w /w). The monomers have a synergistic effect upon each other to take place in the graft copolymer.