Nanocomposite monodisperse polystyrene microspheres (ca. 90 nm) containing homogeneously dispersed silica nanoparticles (ca. 6 nm) have been successfully produced by combining happily the techniques of microemulsion, emulsion and gamma-ray irradiation. The product was characterized with TEM, FTIR, and TGA. A possible formation mechanism of the nanocomposite was proposed.