Composites made by incorporation of silicon oxide (SiO2) or titanium (TiO2) nanoparticles into poly(p-phenylene vinylene) (PPV) have been fabricated and their electrical and optical properties have been investigated. The UV-vis absorption and Raman spectra showed that SiO2 nanoparticles reduced the conjugation lengths of PPV chains, while TiO2 nanoparticles did not. In the case Of SiO2 nanoparticles, the reduction of conjugation length was more noticeable on increasing the oxide concentration or on decreasing the particle size. Fourier transform infrared (FT-IR) spectra showed that both types of nanoparticles also reduced the formation of carbonyl groups in PPV main chains. Current-voltage characteristics measured in the indium tin oxide (ITO)-composite-MgAg diodes exhibit different electrical behavior to the composites depending on the particle size and the nature of the used oxide. The composite-electrode contact morphology, the polymer-dielectric particle contact, and the change in the polymer chain length are the possible explanations for these changes in behavior of the diodes. (C) 2004 Elsevier B.V. All rights reserved.