Monodisperse carboxyl-functionalized polystyrene particles size with range of 0.6~2.1μm were synthesized by two-stage radiation-induced dispersion polymerization of styrene in ethanol/water media using poly (vinylpyrrolidone) (PVP) as the stabilizer and itaconic acid (IA) as a functional comonomer. The resulting carboxylated polystyrene (PS) particles have a narrower size distribution compared with those obtained by one-stage dispersion polymerization. In the two-stage method, the presence of additional IA in the second reaction stage may help to prevent secondary nucleation and to promote the formation of monodisperse particles. The effects of concentration of IA, PVP and solvent polarity on the particle size and size distribution have been discussed in detail. The carboxyl group density on the surface of the copolymer particles has been determined directly by conductometric titration. In order to examine the functionality of the particles, P(St-co-IA)/Co composite microspheres are prepared by repetitious interface reduction reactions.