The graft copolymerization of acrylic acid/methyl methacrylate (AA-MMA) onto poly(ethylene terephthalate) fibres has been studied using benzoyl peroxide (Bz(2)O(2)) as an initiator. The use of MMA as a comonomer increased the amount of AA introduced to the PET fibre up to 60% while the grafting of AA onto fibres alone gave low graft yields. This synergistic effect was found to be at its highest when an AA-MMA mixture having 30% AA (wt.) was used. The grafting increased the diameter and moisture regain of the fibres. The results of dyeability with the disperse dye suggested the diffusion into the fibre structure was moderately difficult when the graft yield reached 15-16%. The decomposition temperature values obtained from thermogravimetric analysis (TGA) showed that the thermal stability of poly(ethylene terephthalate), fibres decreased as a result of grafting.