High-temperature oxidation of sintered beta-FeSi(2) doped with Mn and Co was evaluated at 800 degrees C in air. Amorphous SiO(2) was developed as an oxide scale. Granular epsilon-FeSi also appeared below the SiO(2) scale as a result of consumption of Si in beta-FeSi(2). Growth of the oxide scale on doped FeSi(2) followed a parabolic law and its rate was similar to oxidation of undoped samples. Thermoelectric properties of sintered beta-FeSi(2) were also evaluated before and after oxidation at 800 degrees C for 7 days. There was no significant change in thermoelectric properties after high-temperature oxidation on beta-FeSi(2) sintered bodies.