Abstract: The thermal stability of nanostructure of cold-rolled Ti-15-3 alloy with high reduction was studied by means of TEM and XRD.It is shown that the nanostructure of the cold rolled alloy was very stable at 450℃ and the size was 100-150 nm after holding for 1 200 min.The stability became lower at 550℃ and the nanostructure became unstable within very short time after heating at 650℃ or above.When the nanoscale β alloy were annealed in the two phase region of (α+β),α phase would pin the dislocations and boundries and prevent the growth of nanostructure.The growth of nanograins at relatively low annealing temperatures was associated with the non-equilibrium grain boundaries within the nanostructure.