An iron aluminide (Fe-40 at.% Al) was thermal oxidation (TO)-treated at 1000 degreesC for 30 to 150 h. The mechanical properties (e.g., hardness and elastic modulus), the scratch resistance, the deformation and damage behaviors of the TO-treated surface layers were evaluated using nanoindentation and nanoscratch techniques. It has been found that the TO treatment produced an oxide layer containing alpha-Al2O3 on the iron aluminide surface, which increased the surface hardness (H) and elastic modulus (E-r) but reduced the ratio of E-r/H. This has significantly improved the scratch resistance of the iron aluminide. Longer treatment resulted in a thicker oxide layer and led to further reduced scratch rate and an increased critical load to failure. The scratch resistance has been correlated with the scratch load, the hardness, and the Er/H ratio of the surface oxide layer.