High-temperature oxidation of sintered β-FeSi2 doped with Mn and Co was evaluated at 800°C in air. Amorphous SiO2 was developed as an oxide scale. Granular ε-FeSi also appeared below the SiO2 scale as a result of consumption of Si in β-FeSi2. Growth of the oxide scale on doped FeSi2 followed a parabolic law and its rate was similar to oxidation of undoped samples. Thermoelectric properties of sintered β-FeSi2 were also evaluated before and after oxidation at 800°C for 7 days. There was no significant change in thermoelectric properties after high-temperature oxidation on β-FeSi2 sintered bodies.