In order to search a new process of fabricating TiAl intermetallic compounds with favorable combination of properties, this paper investigated the microstructure and thermal stability of Al-10wt.%Ti powders synthesized by mechanical milling. The experimental results show that Al, Ti particle and grain size decrease rapidly with the increase of milling time, and that the more milling time, the more energy stored in the composite powders. Consequently, the activation energy of the reaction for Al-Ti intermetallics decreases obviously. It is mechanical milling that causes a large number of crystal defects such as dislocations, vacancies, stacking fault and grain boundaries, hence raise the internal energy and the diffusivity. The final equilibrium phase of Al-10wt.%Ti powder which was sintered is DO22-Al3Ti.