The thin films were produced from tetraethoxysilane (TEOS) and TEOS/methanol mixtures by the plasma-enhanced chemical vapour deposition technique in a diode planar reactor capacitatively coupled to a r.f. generator at 13.56 MHz. The optical properties of the films deposited on silicon substrates and on glass substrates were studied by means of spectrophotometry in the visible and monochromatic ellipsometry applied at the wavelength of 632.8 nm. The dependences of the deposition rate, the refractive and absorption indices on the deposition parameters were determined for the substrates mentioned. The X-ray photoelectron spectroscopy analyses were performed for the films deposited on the silicon substrates to find film composition dependences on the deposition conditions.