Cold remote nitrogen plasma (CRNP) selectively reacts with silane-terminated organosiloxane compounds such as 1.1.3.3-tetramethyldisiloxane to give polymeric layers. Deposition rate measurements, FT-IR and Raman spectroscopy were performed. The chemical composition of the deposited film is closely dependent on the reactive gas composition and its flowing conditions. An original effect of dioxygen addition in the nonionic reactive media is pointed out : dioxygen addition leads to a fast and highly hydrocarbonated polymer formation with a nitrogen fixation in a silazane structure. Polymerization is described by a model where =Si - O. type of radicals are the critical reactant. A global mechanism is proposed involving active species of the CRNP in initiation step of hydrogen abstraction and the nitrogen triplet state molecule N2 (A 3SIGMA) in methyl abstraction on =Si. type of free radical. Dioxygen adjunction appears to limit the methyl abstraction steps. The efficient direct oxygen reaction on free radicals leads to an increase of the =Si - O. radical density and, consequently of the average length of the growing polymeric fragments. Nitrogen fixation, involving oxygenated species, is discussed. Under defined conditions, a highly hydrophobic polymeric film is obtained with a volumic mass of 1.34 g/cm3 and a deposition rate of about 12 mg/cm2 h corresponding to a growth rate of 200 angstrom/s.