Kinetics of the reaction O + TEOS (tetraethoxysilane) was studied by means of the ESR method Molecular oxygen was partially atomized by a 13.56-MHz discharge in the quartz tube that passed inside an ESR cavity. TEOS vapors were injected between the discharge and ESR cavity. O-atom loss occurring due to the reaction of atomic oxygen with TEOS molecules was measured and the rate coefficient k(1) of the reaction of O atoms with TEOS molecules was determined The obtained results could be used for deposition process simulations.