A metastable-β titanium alloy, Ti-10V-3Fe-3Al (wt. %), was subjected to thermo-mechanical processing including the compression test at 725 °C, which is below the β transus temperature (780 °C), and at strain rate of 10−3 s−1. The presence of phases was determined using transmission electron microscopy and X-ray diffraction. Although the dynamic recovery took place together with slip, both deformation-induced α” martensite and ω were detected as other operating mechanisms for the first time in metastable-β titanium alloy deformed in α + β region. The volume fraction of stress-induced α” was higher than that of the same alloy deformed at room temperature due to a higher strain applied. Stress-induced twinning was not operational, which could be related to the priority of slip mechanism at high temperature resulted from thermally-assisted nucleation and lateral migration of kink-pairs.