Sol-gel SiO2 - TiO2 multilayers (containing 20 mol% TiO2) have been deposited by spin-coating onto single crystal Si substrates previously covered with a SiO2 buffer layer (approximately 4 micrometers), also prepared by sol-gel. The silica-titania films were first densified at 900 degrees Celsius and were then subjected to selected crystallization heat treatments at 1000 degrees Celsius, in order to precipitate different volume fractions of anatase (TiO2) crystallites, between 2.5 and 15%. The optical loss of these nanocomposites was measured at different wavelengths, using argon ion and He-Ne laser light. The experimental loss values, after removing the intrinsic Rayleigh term and surface scattering, were compared to scattering losses calculated by means of the Rayleigh-Mie theory, for light scattering by spherical particles, which was used to examine the influence of different parameters: radiation wavelength, nanocrystallite size and volume fraction of nanocrystals. The theoretical calculations show that, for the wavelengths of interest ((lambda) on the order of or greater than 1 magnitude), nanocrystallite scattering losses remain below 0.5 dB/cm, even for volume fractions as high as 15%, as long as their diameter is below 11 nm. The experimental results agree reasonably well with the theoretical predictions, considering the approximations made. The extension of the model to the study of residual film porosity led to the conclusion that typical porosity present has a negligible influence on the total waveguide loss.