This work presents the study of the kinetics of the solid-to-solid β→ωiso transformation in Metastable β-Ti alloy TIMETAL LCB by Resonant Ultrasound Spectroscopy (RUS). Metastable β-Ti alloys exhibit various solid-to-solid phase transitions. We focused on the diffusion controlled β→ ωiso phase transition. Particles of ω phase play an important part in thermomechanical treatment because they serve as heterogeneous nucleation sites for precipitation of finely dispersed particles of hexagonal α phase. But it is very difficult to observe in situ the growth of particles of ω phase. Recent works showed that the ω phase significantly influence the elastic constants of the material and the different forms of ω phase have different effects on the elastic anisotropy, as well as on the internal friction coefficients. The RUS method is based on the fact that resonant frequencies of the specimen contain information on elasticity and so RUS provides the complete set of elastic coefficient for large group of materials. It also allows to observe in situ the β→ω phase transformation by the precise measurement of the tensor of elastic constants of polycrystalline samples of TIMETAL LCB alloy during isothermal and non-isothermal ageing at temperatures up to 300 °C. Measured data were interpreted and compared with the the phase field model.