The mechanical behavior and the effect of deformation on the martensitic transformation of Ti₄₄Ni₄₇Nb₉ alloy were investigated in detail by tensile tests and electrical resistance measurements. The tensile behavior at various temperatures, the effect of annealing temperature after cold work and the aging effect were studied. As a whole, the tensile behavior was found to be very similar to that of Ti–Ni binary alloys with low Ni content which shows no aging effect. Superelasticity was found for the first time in the present alloy. The rise of A_s due to deformation was confirmed. However, the effect of deformation vanished after the subsequent reverse transformation, as reported earlier. Deformation generally suppresses the subsequent thermal martensitic transformation. In this study, we also found a remarkable effect promoting the transformation in the 873 K I.Q. specimen, which shows a very narrow hysteresis loop in electrical resistance vs. temperature curve. The hysteresis loop was found to become wider greatly after deformation.