Poly(vinyl alcohol) membrane was coated with organic-silica nanocomposite derived from perhydropolysilazane. For organic composite part, polystyrene-block-poly(4-vinyl phenol) [SP], poly(tert-butyl acrylate-co-2-hydroxyethyl methacrylate) [BA] and poly(butyl methacrylate-co-2-hydroxyethyl methacrylate) [BMA] were used. Water vapor barrier property of coat membrane was measured at relative humidity = 96% by a cup method. The coat films of nanocomposites with SP-silica and BA-silica showed better water vapor barrier property than those of the silica coat film without organic polymer and BMA-silica composites. The surface morphologies of the coat films were investigated by scanning electron microscopy and atomic force microscopy. The addition of organic polymer to silica prevented the crack formation of coat layer on the substrate. (C) 2008 Elsevier Ltd. All rights reserved.