Abstract: The oxidation behavior of Fe-25%Cr-6%Al-RE(rich Lanthanum) alloy in pure oxygen at 1 200℃ has been examined by transmission electron microscopy. It was shown:after oxidation at 1 200℃ for 2 h Lanthanum in alloy precipitated as hexagonal structure La₂O₃ particles at the top of α-Al₂O₃ grains or the grain boundaries in the oxide scale. The aluminium atoms outward diffusion and the lateral growth of the oxide scale are prenvented; during 1 200℃/room temperature thermal cyclic oxidation, rare, earth elements could speed up internal oxidation rate as alumina and lanthanum oxide appeared. A cubic La₂O₃ particles parallel to the grain boundaries in the alloy.