Electron microscopy and X-ray diffraction were used to study phase and structural transformations in a multicomponent (5.05 wt % Mo-4.95 wt % V-3.00 wt % Cr-3.05 wt % Al) metastable beta titanium alloy upon aging after plastic deformation. The alloy is deformed by twinning on the {332} <11 $$(3) over bar > system, and a twinned framework is formed in its structure already at the initial deformation stages. Upon further loading, the twin framework is deformed by secondary twinning, which causes high plasticity of the alloy. Upon annealing, the deformation twins are transformed into the a phase, and the "soft" twin framework is replaced by a "rigid" framework of the alpha-phase plates. Aging increases the yield strength of the alloy, but drastically decreases its plasticity.