The effect of oxygen presence in sputtering chamber on magnetization of thin (approximately 700-800 angstroms) FeCo films was studied by polarized neutron reflectometry. The samples were prepared by magnetron sputtering of the Fe₃₆Co₆₄ alloy onto glass substrates in the presence of oxygen in the sputtering chamber. For a given oxygen content in the sputtering chamber the oxygen concentration in the film decreased with the sputtering rate. The increase in oxygen inside the film was found to decrease its magnetic saturation induction. The exact element depth profiles of the prepared samples was made by Rutherford back scattering (RBS) technique.