Using sol-gel method, poly(vinyl alcohol)/SiO2 hybrid coating materials with an improved gas barrier property could be produced. Phase compatibility between organic PVA segments and inorganic silicate network in the hybrid was evaluated by analyzing FT-IR spectra and investigating the crystallization behavior in terms of X-ray diffraction patterns for the hybrid gels. For the preparation of coating film with barrier property, the biaxially oriented polypropylene (BOPP) substrate was coated with the hybrid sols by a spin coating method. Morphological analysis for the fractured surface of the hybrid gel and the surface of the coated film was performed not only to examine the microstructure of the hybrid, but also to propose evidence for the oxygen permeation behavior through the coated film. It was revealed that an optimum amount of inorganic silicate precursor, TEOS, should be used to obtain high barrier PVA/SiO2 hybrid coating materials with enhanced micro-phase morphology and optical transparency. This homogeneous morphology densified with nano-structured silicate, obtained at optimal conditions, was found to result in a significant increase in the oxygen barrier property of film coated with PVA/SiO2 hybrid by about 50 times relative to the pure BOPP substrate. In addition, the effect of pretreatments of the BOPP substrate surface on the barrier property was also examined.