The long-term oxidation behavior on a Ti-2Al-2.5Zr alloy with and without pre-oxidation oxidized at 300 in an alkaline steam for about 13000h were studied. Some of the samples were subjected to 400°C deionized water steam at a pressure of 10MPa for 72 hours for pre-oxidation. A comparison study has been carried out between the pre-oxidized and without pre-oxidized Ti-2Al-2.5Zr to determine the influence of pre-oxidation upon the properties of oxidation resistance. The result analysis showed that the oxide scales on the Ti-2Al-2.5Zr alloy consisted of Al2TiO5, TiO2, Ti3O5, Ti2O3, Al2O3 and TiO. The oxidation kinetics showed that the weight gains of the pre-oxidized samples were much less than that of the without pre-oxidized samples. The AES results showed that the whole thickness of the pre-oxidized sample thinner than that of the without pre-oxidized one, in contrast the pattern for the stable oxide scale was reversed, i.e. the pre-oxidized sample was much thicker. It is thought that pre-oxidation is an effective method to enhance the oxidation resistance of Ti-2Al-2.5Zr.