Poly(vinyl alcohol)/silica organic inorganic hybrid composites were prepared by using sol-gel technique. Tetraethoxysilane was used as the precursor for silica. The reaction was carried out in an aqueous medium having a pH of 1.5 with concentrated hydrochloric acid, used as the catalyst. All the composites were optically clear. Interaction at organic-inorganic interfaces due to hydrogen bonds was speculated from infrared spectroscopic analysis of the hybrid composites. Transmission electron microscopic studies revealed the existence of silica nanoparticles, uniformly dispersed in the organic matrix, which were found to grow in size with increase in tetraethoxysilane loading in the composites. Uniform dispersion of silica particles within the hybrid nanocomposites was also supported from the energy dispersive X-ray mapping of silicon. Dynamic mechanical properties exhibited substantial mechanical reinforcements due to the dispersion of nanosilica particles in the matrix. The results were further supported by significant improvements in the Young's modulus and the tensile strengths of the samples. All the hybrid composites demonstrated excellent water resistance. (c) 2005 Springer Science + Business Media, Inc.