Abstract: The silicon dioxide (SiO₂ ) / polystyrene ( PS) composite microspheres were prepared by dispersion polymerization in ethanol/ water medium. The process of dispersion polymerization was investigated , and the kinetics ofdispersion polymersion with nano-SiO₂ in the reaction system was studied. The samples were characterized by microscopy techniques (SEM ,TEM) . It is shown that nano-SiO₂ particles are encapsulated by PS af ter dispersion polymerization in ethanol/ water medium using polyvinylpyrrolidone ( PVP K-30) as stabilizer. The average size of thecomposite microsphere is 1.25μm and the dispersion coefficientεis 0.035. The effect s of stabilizer concent ration onthe size of the microspheres were studied.