Effect of high pressure on the lamellar spacing and mechanical properties of Ti-48Al alloy was investigated. The results indicate that when solidified under high pressure, the lamellar spacing decreases with the increasing of pressure. The average lamellar spacings are 495, 345 and 227 nm, respectively, when solidified under normal pressure, 2 GPa and 4 GPa. Also the microhardness increases with the pressure increasing. It provides a new way to refine the lamellar structure.