Abstract: Directionally solidified samples of arc-melting Ti-48Al-8Nb(at%) alloy were prepeared through Bridgeman unidirectional solidification technique equipment.The effects of different drawing velocities on the structure of liquid-solid interface and the structures of the transition zone and steady state were observed.The columnar grains grow well along the drawing direction at different drawing velocities.The solid-liquid interface transformed from celluar form to dendritic form when drawing velocity increased from 8μm/s to 50μm/s.The secondary dendrite arm spacing and the interlamellar spacing decreased with the increasing of drawing velocity.In the same time,the propotion of α₂/γ lamellar perpendicular to the growth direction increased observably with the increasing of drawing velocity.