Grafting of poly(ethylene terephthalate) fibers (PET) with 2-methyl-5-vinylpyridine (MVP) was carried out using γ rays and benzoyl peroxide independently for the initiation of grafting. The poly(MVP)-PET graft copolymers were analyzed for density, moisture regain, and dyeability. Radiation-induced grafting yielded copolymers with densities and moisture regain appreciably higher than those produced by benzoyl peroxide. The same results occurred when acid dyes were used. The behavior of (MVP)-PET graft copolymers towards some reactive dyes was also studied. The extent and rate of dyeing were dependent of pH of the dye bath, nature of the dye and the magnitude of grafting. Dyeing occurs through formation of salt linkages between the pyridine moieties and the solubilizing groups (usually sulfonate groups) in the dye molecule.