Taking two metastable $\beta$-titanium alloys VT22 (Ti—5 (% wt.) Al—5V—5Mo— 1Fe—1Cr) and Ti—3Al—4.5Fe—7.2Cr as program materials, the influence of $\beta$-grain size, phase composition, and strain rate (in the range of $3.20\cdot10^{-5}$ up to $1.81\cdot10^{-1}$) on alloys’ mechanical behaviour is investigated. The mechanical behaviour of both alloys in as-quenched single-phase $\beta$-state is similar to another metastable $\beta$-alloy TIMETAL-LCB: ductility and tensile toughness are monotonously decreased with strain rate. Ageing causes increase in strength and decrease in ductility, whereas the drop of the latter is the most pronounced in both the coarse-grained VT22 alloy and the Ti—3Al—4.5Fe—7.2Cr one regardless of grain size. As suggested, the reason of this effect is the formation of thin layers enriched by $\beta$-stabilizing elements located close to grain-boundary $\alpha$-phase. Taking into account drastic embrittlement of Ti— 3Al—4.5Fe—7.2Cr alloy, which contains only $\beta$-eutectoid alloying elements, this enrichment can lead to the precipitation of intermetallics.