Au/SiO₂ nanocomposite films, studied in this work, were prepared by RF-magnetron sputtering technique on glass substrate at room temperature under two different substrate temperatures (Ts), and subsequent heat treatment. For the deposited sample at T_S = 25℃, no apparent surface plasmon resonance peak could be observed. After annealing, optical absorption spectrum of the Au/SiO₂ thin films showed a broad absorption band around 500 nm relating to gold nanoparticles without any modification in the position of the SPR and the size of particles. For the series deposited at T_S = 400℃, the surface plasmon resonance (SPR) was found at 500 nm. After heat treatment it’s redshift from 500 nm to 503 nm, while the size increases from 2.01 nm to 2.3 nm. We have also shown that, as the AuNPs are embedded in silica films, the small nanoparticles size have a slightly larger expansion coefficient than for bigger one.