The formation of covalent bonds between silanols in copolymer and those in silica prevents organic-inorganic phase separation. Two series of hybrid composite materials, poly(vinyl acetate-co-vinyl trimethoxysilane)/TEOS and poly[vinyl acetateco-3-(trimethoxysilyl)propyl methacrylate]/TEOS, were fabricated using a modified sol-gel process. The hybrids were transparent. Two kinds of silane coupling agents, vinyl trimethoxysilane (VTS) and 3-(trimethoxysilyl)propyl methacrylate (gamma -MPS), were used to prevent macrophase separation through formation of covalent bonds. Thermal analysis showed that gamma -MPS was more effective than VTS for the formation of covalent bonds. Enhancement of thermal stability of the hybrids was investigated by thermogravimetric analysis. Photomicrographs of scanning electron microscopy and images of atomic force microscopy indicated that inorganic silica particles were homogeneously dispersed in less than 50 nm in organic matrix. The morphological properties of hybrids were strongly dependent on the organic-inorganic composition.