A novel microphase-inversion method was proposed for the preparation of TiO2-SiO2/poly(methyl methacrylate) core-shell nanocomposite particles. The inorganic-polymer nanocomposites were first synthesized via a free-radical copolymerization in a tetrahydrofuran solution, and the poor solvent was added slowly to induce the microphase separation of the nanocomposite and result in the formation of nanoparticles. The average particle sizes of the microspheres ranged from 70 to 1000 nm, depending on the reaction conditions. Transmission electron microscopy and scanning electron microscopy indicated a core-shell morphology for the obtained microspheres. Thermogravimetric analysis and X-ray photoelectron spectroscopy measurements confirmed that the surface of the nanocomposite microspheres was polymer-rich, and this was consistent with the core-shell morphology. The influence of the synthetic conditions, such as the inorganic composition and the content of the crosslinking monomer, on the particle properties was studied in detail. (c) 2006 Wiley Periodicals, Inc.