Two methods were used to prepare the silica/poly(2-hydroxyethyl methacrylate) (PHEMA) nanocomposites: one was the direct mixing of colloidal silica with PHEMA using methanol as a co-solvent (colloidal silica/PHEMA) and the other was the adding of the inorganic precursor, tetraethyloxysilane (TEOS), to the PHEMA/methanol solution, followed by the sol-gel process with an acid-catalyst (TEOS/PHEMA). The structure of the colloidal silica/PHEMA hybrid consisted of nano-silica uniformly dispersed in the PHEMA phase with slight inter-molecular hydrogen bonding. The structure of TEOS/PHEMA hybrid was similar to a semi-interpenetrated network with PHEMA chains tethered into the nano-silica network by inter- and intra-molecular hydrogen bonding. Consequently, the TEOS/PHEMA hybrid gels exhibited a smoother surface, higher transparency, and better thermal stability than the colloidal silica/PHEMA hybrid gels. (C) 2005 Elsevier Ltd. All rights reserved.