The paper considers the process of oxidating an alloy of the Fe-25Cr-35Ni-0,45C-Si-Nb system at air temperatures of 400-1150 °C, which has been experimentally studied. The study reveals the nanoscale level of the oxidation process and defines its character and kinetics. It is established that the oxidation process provisionally consists of three stages. It is shown that kinetics of the high-temperature alloy oxidation is determined by processes of scale formation and scale’s structure degradation. For a reliable assessment of an operation resource in heat-resistant Fe-25Cr-35Ni-0,45C-Si-Nb alloys, it is necessary to conduct preliminary pilot research on their corrosion resistance in each case.