The processes of structure formation and phase transformations taking place in metastable β-alloy Ti-15Mo in case of torsion under high pressure at room temperature have been studied. By the methods of transmission electron microscopy and X-ray structure analysis, it has been found out that grain refinement is accompanied by the phase transformation β↔ω and the nonmonotonic changing of a volume fraction of ω-phase with increase in a deformation ratio. A ω-phase role in formation of strength and elasticity properties of the alloy is discussed. It was determined that formation of nanostructure with a minimum content of ω-phase made possible to obtain a considerable strengthening with keeping a relatively low modulus of elasticity of Ti-15Mo alloy.