Abstract: The effects of pre-aging on the microstructural evolution and mechanical properties of a near β type Ti-10Mo-6Zr-4Sn-3Nb (Ti-B12) biomedical titanium alloy were investigated.The results show that a large number of ellipsoidal isothermal ω phases are uniformly precipitated within the parent β phase when the alloys are pre-aging treated at 325 ℃and 425 ℃with the holding time from 0.5 h to 8.0 h, respectively.The size of ω phases gradually increases and the density of them progressively decreases with the increase in the pre-aging temperature and holding time. Based on the effect of isothermal ω transitional phase assisted α phase nucleation and refinement, the higher density, smaller size and more dispersed distribution of secondary α phases can be obtained at the lower pre-aging temperature and shorter pre-aging time. Moreover, the strength can be improved and the better plasticity can be achieved via further refining the dimension and increasing the density of secondary α phases after pre-aging. However, the strengthening effect is no longer obvious when the pre-aging time increases to a certain value.