Gamma radiation-induced grafting of styrene into FEP films was investigated by the preirradiation method. The degree of grafting was found to be strongly dependent on the synthesis conditions, such as radiation dose, monomer concentration, crosslinker, temperature, and film thickness. The order of dependence of the rate of grafting on pre-irradiation dose and monomer concentration was found to be 0.64 and 1.90, respectively. The activation energy for the grafting in the temperature range of 50-80-degrees-C was determined to be 27.9 kJ/mol. A negative first-order dependence of grafting on film thickness was observed. The results suggest that the initial grafting takes place at the film surface and proceeds to the middle by progressive diffusion of monomer through the polystyrene grafted layers.