The effect of heat treatment and thermal exposure on the microstructure and mechanical properties of non-burning β titanium alloy Ti-25V-15Cr-2Al-0.2C (mass fraction, %) was investigated. It is found that the amount of α precipitation in samples after solution treatment followed by air cooling increases with increasing solution temperature. After solution treatment, the alloy was subjected to two different heat treatments to stabilize the material. The results show that the single ageing treatment(700 ℃, 4 h, AC) leads to a large amount of α precipitation, while the triplex treatment(850 ℃, 2 h, FC+700 ℃, 6 h, FC+540 ℃, 6 h, AC) significantly suppresses the formation of α precipitates. It is more important that after long-term exposure at 540 ℃(the expected application temperature) samples heat-treated by the triplex treatment have markedly higher ductility than those given the single aging treatment. The intermetallic compound TiCr2 is observed in samples after long-term exposure, which further degrades the ductility of the alloy.