Abstract Ni 51 Ti 49 alloy prepared by rapid solidification was trained through constraint-aging to possess two-way shape memory effect (TWSME), so as to make a purpose-designed bio-actuator. Influences of aging conditions (i.e., temperature, time and constraint stress) on the transformation behavior and shape memory effect of the alloy were investigated to obtain the desired functional property. Results show that the rapidly solidified Ni 51 Ti 49 alloy strip followed by constraint-aging at 400 °C for 100 h exhibits an optimized TWSME. With a high recovery ratio of 92.9% and a pre-designed transformation temperature range of 35–55 °C, the so-obtained Ni 51 Ti 49 alloy has great potential to be used as the bio-actuator. Results of metallographic analysis demonstrate that the microstructure of the above treated Ni 51 Ti 49 alloy strip consists of fine elongated grains with B2 preferred orientation along the direction of the maximum cooling rate. Such fine grains with preferred orientation restrict the size of Ni 4 Ti 3 precipitates to nano-scale during aging treatment under an optimized condition. Meanwhile, the constraint stress during the aging process leads to preferred orientation of Ni 4 Ti 3 precipitates according to the stress states in different regions of the alloy. Such coherent and uniquely distributed Ni 4 Ti 3 precipitates in the NiTi alloy contribute to significant improvement of TWSME.