An ethylene/vinyl alcohol copolymer (EVOH) with superior barrier properties was used as an organic component to prepare EVOH/SiO2 hybrid materials with improved gas barrier properties with a sol-gel method. As a silane coupling agent, 3-isocyanatopropyl triethoxysilane (IPTES) was used to promote interfacial attraction between the organic EVOH segments and the inorganic silicate network in the hybrid. The phase compatibility was evaluated by analysis of Fourier transform infrared spectroscopy and phase morphology and the optical properties of the hybrids. We confirmed that the addition of the silane coupling agent IPTES up to some level of content resulted in enhanced phase compatibility and optical transparency of the nanostructured hybrid material with a homogeneous phase morphology exhibiting no microphase separation. For the preparation of the monolayer coated film, the biaxially oriented polypropylene substrate pretreated with a corona was coated with the hybrid sols by a spin-coating method. The oxygen permeation behavior through the coated film was examined with various contents of the silane coupling agent IPTES and inorganic silicate precursor tetraethoxyorthosilicate in the hybrid system. Consequently, it was revealed that an optimum range of IPTES and tetra ethoxyorthosilicate contents was required to produce high barrier EVOH/SiO2 hybrid materials with a stable homogeneous microstructure and enhanced optical transparency. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 115: 1663-1670, 2010