Stainless steel is widely used as a corrosion-resistant material. However, stainless steel corrodes at high temperature (573 K ~) due to the oxidization and grain boundary corrosion. To delay the oxidation at high temperature, coating of gas barrier film will be useful method. The purpose of this study is to improve the corrosion-resistant of SUS304 at high temperature by coating transparent SiOxNy film which has gas barrier properties. In addition, the influence of inlet gas mass flow rate ratio (N2/Ar+N2) on the oxidation properties at 773 K was examined. The SiOxNy films were deposited onto polished SUS304 by unbalanced dc magnetron sputtering apparatus. To examine the oxygen transmission rate (OTR) of SiOxNy films, PET was also used as substrate. The results showed that good OTR was obtained for N2/Ar+N2 < 0.12 on PET substrate. The similar tendency was obtained for SUS304 deposited film heated up to 773 K.