The structure of deformed titanium β-alloys of transition class is studied. A model of anomalous twinning over the {332} ≥113≤ system typical for these alloys is developed. An explanation of the low stress of nucleation and growth of such twins, the ease of their intersection with each other, and the blocking action of the twin boundaries in slip deformation is given within the framework of the model. The effect of aging after cold plastic deformation on the yield strength of titanium β-alloys strained by twinning over the {332} ≥113≤ system is studied. © 2006 Springer Science+Business Media, Inc.