In this paper, aging response of a recently developed near b Ti-25Nb-2Mo-4Sn (wt%) alloy with high strength and low modulus was investigated intensively. The experimental results from X-ray diffraction and transmission electron microscopy showed that the aging production of the Ti-2524 alloy was (bto) or (bta) even under the same aging treatment condition, depending on the pre-treatments prior to the aging. Solid evidence confirmed the competition between stable a phase and metastable o phase during the decomposition of b phase on aging. Different aging response of Ti-2524 alloy can be attributed to high-density dislocations and grain boundaries which suppress the formation of o, and alternatively promote a phase formation. This provides a thermo-mechanical approach to inhibit deleterious o phase formation and assist fine a phase precipitation. Upon an appropriate aging treatment, superior mechanical properties of high ultimate tensile strength (1233 MPa) and low elastic modulus (77 GPa) were achieved in Ti-2524 alloy.