The effect of thermomechanical treatment on the structure and phase transitions of the aging shape-memory Ti–51 at % Ni alloy has been studied. Mechanical tensile tests were performed in combination with optical and electron microscopic and X-ray diffraction studies. An ultrafine grained (UFG) structure was created in the alloy by multipass-rolling plastic deformation and further annealing. It was established for the alloy to have a high level of mechanical properties (ultimate tensile strength up to 1550 MPa at a relative elongation of more than 20%) owing to a highly disperse phase of precipitation with the formation of an UFG structure due to recrystallization.