Polystyrene/poly(styrene-poly(ethylene glycol) monomethacrylate) or PS/P(S-PEGMMA) composite polymer particles in the size range of one to several microns were prepared by seeded copolymerization. Monodisperse micron-sized polystyrene (PS1) particles were first prepared by dispersion polymerization, which were then used as seed particles to carry out seeded copolymerization with styrene and poly(ethylene glycol) monomethacrylate (PEGMMA). Several micron-sized polystyrene (PS2) particles were prepared from monodisperse micron-sized PS1 particles by a modified activated swelling method. These PS2 particles were finally used as seed particles to carry out seeded copolymerization with styrene and PEGMMA. For comparison, some swelling experiments were also carried out in the presence of macromonomer. The size distribution and particle morphology were analyzed by light and scanning electron microscope. The FTIR-ATR technique was used to detect the presence of poly(ethylene glycol) or PEG units on the surface of particles. The results indicate that seeded copolymerization in the final step is the best way to prepare several micron-sized composite polymer particles containing PEG on the surface.