As the object of study in this work, we used the two-phase (α + β)-titanium alloy VT23 in the delivery state. A preliminary heat treatment of the samples was carried out at different temperatures, including annealing, quenching at various temperatures, and subsequent cooling in water in order to obtain different stability of the β-phase. Using the methods of optical microscopy, X-ray phase analysis and mechanical tests, microstructure, phase composition and mechanical properties of samples of the VT23 two-phase titanium alloy with different β-phase stability were studied. The parameters of the cubic lattice of the β phase after various heat treatment modes are determined, the dependence of the lattice period on the quenching temperature due to the change in alloying system is established. The results of uniaxial tensile and impact bending tests of samples of this alloy at room temperature showed that an increase in quenching temperature from 800 to 860 °C gives a rise in strength, ductility, impact strength and crack propagation characteristics. Methods of instrumental impact tests revealed the effect of quenching temperature increasing on the type of loading diagram and characteristics of impact strength. A fractographic study of the fracture surface of VT23 alloy specimens after impact tests showed that the observed change in the type of loading diagrams is in good agreement with the change in the fracture mechanism and, in particular, with the elimination of intergranular structure on impact specimens fracture surface after increasing the quenching temperature to 860 °C, which contributes to the destabilization of the β phase in relation to stress-induced martensitic transformation. It was found that crack growth in samples with a metastable β-phase occurs along the boundaries of martensitic plates and their packs.