The polymer precursors containing polyvinylsilane (PVS) with polycarbosilane (PCS) in coating form were prepared. As the content of PVS increases, the onset temperature of the precursor oxidation decreases and the surfaces formed after the oxidation become smooth and hard. The role of SI-H bonds in the PCS-PVS systems during the oxidation is quantitatively analysed on the basis of the absorption of the SI-H stretching band in the precursor spectra. In the blended systems, the oxidation of the Si-H groups forms the dense crosslinked polymer layer which limits the oxygen diffusion into the precursor interior.