Monodisperse poly(methyl methacrylate) particles were prepared directly by radiation-induced dispersion polymerization in hexane-ethanol media using vinyl terminus polysiloxane (PSI) macromonmer as a polymerizable stabilizer at room temperature. This method takes advantage of the specialties of radiation-induction, which may result in the formation of uniform polymer particles. The gel effect is evident from the polymerization kinetics curves. Vinyl terminus PSI macromonomer acted as not only a comonomer, but also as a stabilizer. The characterization of PMMA particles was carried out by the scanning electron microscope (SEM), FT-IR, H-1-NMR and X-ray photoelectron spectroscope (XPS). XPS results show that the graft PSI macromonomers were anchored on the surface of PMMA particles to provide a steric stabilization to the PMMA particles.