Cooling rate has drastic effects on the continuous cooling transformation of Ti-45Al-5Nb and Ti-45Al-5Nb-0.3Y alloys. Furnace cooling (FC) leads to the fully lamellar microstructure. Air cooling suppresses the lamellar transformation by the α→γm reaction. Oil cooling leads to the extremely fine lamellar microstructure. At a higher cooling rate (such as water cooling), the α2 phases are predominant. By air cooling a feathery structure disappears and the α2 phase increases. By water cooling, the extremely fine lamellar regions located at initial α2 grain boundaries are smaller and increase for the Ti-45Al-5Nb-0.3Y alloy. Y addition has slight effect on the phase transformation of Ti-45Al-Nb alloy.