Silica/titania binary inorganic component was synthesized by a nonhydrolytic sol-gel method. Fourier transform infrared spectroscopy (FT-IR) and transmission electron microscopy (TEM) results indicated that titania was stabilized by silica because of the formation of a connecting structure, which would greatly restrain the high aggregation tendency of titania nanoparticles. The thermal stabilities of the PMMA/silica/titania ternary nanocomposites were measured by thermo-gravimetric analysis (TGA). Although the solvent extraction results confirmed that there were no covalent bond interactions between polymer and inorganic phases, the trace amount of stabilized titania improved the thermal and thermo-oxidative stabilities of PMMA because titania/silica nanoparticles may have ability to trap the free radicals generated in the degradation of PMMA.