A series of Poly(imide siloxane) (PIS)/silica (SiO2) hybrid nanocomposites with C-Si covalent bonding between the homogeneous PIS copolymer and SiO2 have been successfully synthesized. The PIS copolymer synthesized in this study is characterized by the coexistence of two segments: the polyimide segment and polydimethyldiphenylsiloxane segment, and the latter are specially featured with the introduction of a diphenyl group for improved homogeneity. The PIS/SiO2 hybrid nanocomposites were prepared from 3,3,4,4'-bezonphenone tetracarboxylic dianhydride (BTDA), 2-2-bis[4(3-aminophenoxy)phenyl] sulfone (ni-BAPS), and vinyl-containing alpha,omega-bis(aminopropyl)polydimethyldiphenyl siloxane (APPPVS) oligomer to form vinyl siloxane-containing poly(amic acid) (PAAVS). This copolymer was further reacted with trimethoxyvinylsilane (TMVS), 2,2'-azobis-isobutyronitrile (AIBN), and tetraethoxysilane (TEOS). The PIS/SiO2 hybrid nanocomposites exhibited a series of properties unlike traditional composites, and the nano sized inorganic particles have resulted in a transparent hybrid when the SiO2 content was less than 12 wt %. The Young's modulus and tensile strength of the PIS/SiO2 hybrid nanocomposites increased with increasing SiO2 content, whereas, the elongation at break was only slightly affected. The structure of the hybrids was characterized by FTIR, 29 Si-NMR, 'H-NMR, and C-13-NMR, as well as SEM and TEM. The thermal properties of the PIS/SiO2 hybrid nanocomposites were investigated with DSC, TGA, and DMA studies. (c) 2007 Wiley Periodicals, Inc.