The phase transformation and microstructure in solution-treated Ni50Ti47Ta3, Ni50Ti45Ta5, Ni49Ti46Ta5 shape memory alloys (SMAs) have been investigated. Two different second-phase particles, (Ti,Ta)(2)Ni and a tantalum-rich solid solution (beta-Ta) mostly located at grain boundaries are observed. These Ni-Ti-Ta alloys undergo a one stage B2 <-> B19'transformation. Experimental results indicate that the Ta atoms are suggested to replace Ti atoms, instead of Ni atoms in these alloys. The transformation temperatures depression of Ni-Ti-Ta alloy is more than that of NiTi alloy under the same number of thermal cycles due to the presence of more second-phase particles. The above 4% deformation might induce plastic strain for the beta-Ta. The Ni-Ti-Ta alloys exhibit a wide transformation hysteresis compared to NiTi binary alloys. (c) 2005 Elsevier B.V. All rights reserved.