The high temperature oxidation behavior of BT25Y titanium alloy was studied at 600 ℃, 700 ℃and 800 ℃. The thermodynamics and kinetics of the alloy oxidation were calculated by the method of continuous oxidation weight gain, the oxidation rate constant and the oxidation activity. The phase composition, surface and cross-section morphologies and elemental distribution of the oxide scale were respectively investigated by XRD, SEM and EDS. The results showed that BT25Y titanium alloy exhibited good oxidation resistance at 600 ℃and 700 ℃, and their oxidation kinetics curves followed the parabolic law. The continuous oxide scale composed of fine TiO₂ and Al₂O₃ particles can effectively prevent oxygen from infiltrating into the matrix and then remarkably reduce the oxidation rate. At 800 ℃, the oxidation behavior of the BT25Y titanium alloy was catastrophic, and its oxidation kinetics approximately followed the linear law. The oxide layer was alternately composed of Al₂O₃ layer and TiO₂ layer, and the oxidation film was loose and porous, which cannot effectively prevent the diffusion of oxygen into the matrix.