The size effect of nanoparticles on the conjugated polymer was investigated in terms of the optical and electronic properties of poly(p-phenylenevinylene) (PPV) and PPV/SiO2 nanocomposites. PPV/SiO2 nanocomposites were prepared by mixing PPV precursor and SiO2 sols with 5 and 19 nm. The conjugation length of the nanocomposite prepared using nanoparticles with 5 nm is much shorter than that of PPV. The nanoparticles with the similar size (5 nm) to the conjugation length of PPV result in an increase of morphological disorder of PPV, while the nanocomposite prepared using nanoparticle with 20 nm shows the decrease of disorder. Therefore, the current density of the device using nanoparticle with 5 nm was lower than that of PPV, while the nanocomposite prepared using nanoparticle with 20 nm shows enhanced current density. (C) 2004 Elsevier B.V. All rights reserved.