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Precipitation behavior of α-phase and its influence on mechanical properties has been systematically investigated in Ti-6Cr-5Mo-5V-4Al metastable β-Ti alloy by comparing the double aging and the single aging. The microstructural characterization shows that the quenched sample consists of equiaxed β-grains. After the following low-temperature pre-aging, dense clusters composed of numerous α nano-laths evenly distribute inside β-grain interiors, while there are precipitate free zones (PFZ) around β grain boundaries. This precipitation feature between β-grain interiors and their grain boundaries is inherited into the later high-temperature aged samples. It can be seen that fine equiaxed α precipitates homogeneously distribute in β-grain interiors but the α-phase exhibits a coarse plate shape adjacent to β-grain boundaries. On the contrary, the α-plates distributes much more evenly in the single-aged microstructure although the plates have larger dimensions. Tensile testing shows that the ultimate tensile strength can be tuned up to ~1630 MPa but accompanied by the degradation of ductility (~2%). The ultra-strength originates from the significant precipitation-strengthening effect as a result of the precipitation of α-particles at the submicron- and nano-scales, and the lost ductility can be attributed to the premature intergranular fracture caused by deformation localization along β-grain boundaries.