A β titanium alloy Ti-6Mo-5V-3Al-2Fe(wt.%) was designed in terms of d-electron alloy design method. Aging treatment was performed at various temperatures ranging from 450℃ to 600℃ for 4h to study the effect of aging temperature on microstructure evolution and tensile properties. The results show that the secondary α phase with smaller size and inter-particle spacing formed under ω-assisted nucleation mechanism at the aging temperature of 500℃. The highest ultimate tensile strength of 1510MPa is obtained due to the strengthening of fine acicular secondary α phase within β grain, while poor elongation of 4.6% is found as a result of the inevitable precipitation of α phase at grain boundary and the formation of precipitate free zone near grain boundaries. Fine secondary α precipitates tends to coarsen with the increasing aging temperature. Coarse α precipitates can bring about broad inter-particle spacing and can result in less α/β interfaces that act as effective dislocation barriers. The increase of aging temperature leads to the variation of tensile properties, i.e. the strength decreased while ductility changed in opposite way. A considerable improvement of elongation to 12.2% is achieved by increasing aging temperature to 600℃, in association with the formation of parallel secondary α laths near β grain boundaries and broad inter-particle spacing of secondary α phase within β grains.