The surfaces of polystyrene (PS) beads were functionalized by radiation-induced graft polymerization. PS beads were gamma-irradiated to generate active species such as peroxides. The graft polymerization of acrylic acid on the irradiated PS was conducted to prepare the poly(acrylic acid)-grafted PS beads. The experimental results revealed that the surfaces of the PS beads were covered with poly(acrylic acid) successfully. The grafting of poly(acrylic acid) onto the PS beads was finally confirmed by a fluorescence labeling method.