The isothermal oxidation behavior of sintered Fe-20Cr alloys with various amounts of Y₂O₃ and La₂O₃ dispersion was investigated in the temperature range from 1273 to 1473 K in air. Dispersion of Y2O3 and La2O3 significantly improved the oxidation resistance. The amounts of Y₂O₃ and La₂O₃ dispersion needed to suppress the break-away oxidation increased with increasing oxidation temperature. The improvement effect of La₂O₃ on the oxidation resistance was stronger than that of Y₂O₃. The grain size of the alloy decreased with increasing the amounts of Y₂O₃ and La₂O₃ dispersion. However, there was no apparent correlation between the oxidation resistance and the grain size of the alloy. The results of IMA analyses showed that the composition of the Cr₂O₃ scale formed during the early stage of oxidation was strongly dependent on the amounts of Y₂O₂ and La₂O₃ in the alloy.