Alumina films containing gold nanoparticles (NPs) were grown by magnetron radio frequency (rf) sputtering technique. They were investigated by transmission electron microscopy (TEM), X-ray diffraction (XRD) and optical absorption spectroscopy. It is suggested that the increase of the contrast of surface plasmon resonance band after annealing is connected with increasing of electron free mean path in Au NPs rather than with change in particle size distribution. The absorption spectra of the nanocomposites have been modelled taking into account a correction of the dielectric constant for electron mean free path limitation.