Weblike aggregates of Si nanocrystals and tungsten oxide nanoparticles are produced by a laser vaporization controlled condensation technique. XRD, FTIR, and Raman results confirm that the Si nanoparticles have a diamond-like crystalline structure and WO3 nanoparticles exhibit a monoclinic crystalline structure. Due to the quantum size effect, the band gaps of Si nanocrystals and WO3 nanoparticles shift to higher energies by 0.68 and 0.55 eV, respectively, from the bulk values. The red emission of Si nanocrystals is quenched by adding successive amounts of the WO3 nanoparticles to Si nanoparticles suspended in a methanol solution. The quenching follows Stern-Volmer kinetics and the quenching rate constants are 14.1 x 10(6) and 3.2 x 10(6) (Ms)(-1) for WO3 and W2O5, respectively. The quenching mechanism is explained by an electron transfer from the CB of the Si to the CB of the WO3 nanoparticles.