Abstract: Steam oxidation tests were conducted on Sanicro25 heat resistant austenitic steel for boiler tube under 27 MPa at different temperatures(650,700℃) for different oxidation times (200,500,800,1 300,2 000 h). The surface and cross section morphology, surface phase composition and oxidation resistance of the test steel were studied. The results show that with the temperature and oxidation time increasing, the thickness of oxide film on the surface of test steel increased, and the steam oxidation resistance decreased. After oxidation at different temperatures for 2 000 h, the inner layer of the oxide film on surface of the test steel was composed of (Ni,Fe)Cr₂O₄ and Cr₂O₃, and the outer layer was composed of Fe₃O₄; while at 700℃, the inner and outer layers contain Cr_1.3Fe_0.7O₃ and (Ni, Fe)Cr₂O₄, respectively. A dense and continuous oxide film was formed on the surface of the test steel.