A series of Ti-Al-Sn-Zr-Mo-Si-Nd alloys with various content of Al were solution treated in alpha+beta phase field and air-cooled. The precipitation of alpha (2) phase in cooling was investigated by transmission electron microscopic analysis. The precipitation characteristic of alpha (2) phase was discussed. The precipitation of alpha (2) phase would proceed by the nucleation and growth of alpha (2) phase dependent on the diffusion of Al atoms. And a comparison on the difference of precipitation of alpha (2) phase was carried out under the conditions of air-cooling and quenching in water. The investigation showed that the air-cooling and even quenching could supply enough time for the precipitation and growth of alpha (2) phase when Al content reached a certain value even though far away from the stoichiometric composition of Ti3Al.