The heat-resistant Ti alloys have been developed to replace Ni-based superalloys conventionally used for discs and blades in the compressor part of jet engines. DAT54 is a newly developed near-alpha Ti alloy in Japan, is serviceable up to 600°C. Titanium has a high solid solubility limit of oxygen and is susceptible to oxygen. Therefore, a systematic study was carried out at different temperatures to examine the degradation of the titanium alloy DAT54 due to oxidation. Test specimens were exposed at 500°C for 100 h or at 600°C for 500 h. Tensile tests were carried out on both as-received and exposed specimens for comparison between ambient and elevated temperatures. To clarify the influence of surface oxidation, we also examined the mechanical properties of oxidation-layer-removed specimens. Tensile properties of the oxidized specimens at and above 200°C were comparable to those of as-received specimens. However, a dramatic loss in elongation at room temperature was observed. The oxidized specimens form cracks on the brittle rutile layer in the elastic region. At room temperature, those surface cracks could propagate easily through the α-case and the oxide layer as well , because deformation of crack tips to a dull state did not occur due to their brittleness. The notched tensile strength was also shown to be sensitive to oxidation. A creep test was performed under the stresses of 100 and 200 MPa at 600°C. Creep strength was improved after the oxidation, probably due to further precipitation of Ti₃Al in the alpha phase. We found that the oxidation-resistant coating dramatically decreased the creep rate and increased the creep rupture life.