The aim of this paper is to analyze the protective character of Si x O y C z coatings deposited on steel. Coatings were deposited by r.f. plasma assisted chemical vapour deposition using methyltrimethoxy-silane (MTMOS) as precursor in a gaseous mixture of O 2 . The process is developed in two stages, first with the substrate at 500 ยฐC and in the second stage with the substrate at room temperature. The first stage is made with the mixture of O 2 and MTMOS, in the second stage a potential of BIAS in the substrate without varying the mixture of gases is added shrouds of the plasma. Surface chemical and morphological characterization of coatings was carried out by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and corrosion test measurements. The corrosion protective behaviour of the film was determined by potentiodynamics polarization curves with coated probes and without coating, in 5% H 2 SO 4 and NaCl 0.1 N solution in nitrogen atmosphere, at room temperature. The new process was successful in producing coatings with good adhesion and the properties are compatible with good corrosion resistance. The deposition process and the film properties are discussed.