The development of microstructure during the aging of Ti-10V-2Fe-3A1 alloy in the β and (α+β) solution-treated and quenched conditions was investigated. The results showed that the isothermal holding below 400℃ yielded homogeneously distributed, spherical ω-phase particles. Fine α aggregates are formed uniformly within β grains by nucleating at ω particles or β/ω interfaces. At higher temperatures, thin martensite plates decomposed in water-quenched condition. The formation of ω phase was avoided and coarse α-phase plates directly precipitated from the β matrix. The highest hardness values were found when the alloys were aged at 400℃ for 8 h. The significance of the observations was discussed in terms of the effect of aging on the precipitations and property.