Deformation processes in thermomechanically loaded nanocrystalline NiTi wires are slightly different from those in single crystals and large grain size polycrystals because of their compound twinned martensite microstructure [Waitz, 2005; Molnarova, 2021]. Microstructure and properties of nanocrystalline NiTi wires can be controlled by fabricating samples with a desired grain size, therefore electropulse treatment was used to obtain wires according to the correlation between pulse time and microstructure. In contrast to superelastic nanocrystalline NiTi wire [Chen, 2019], no systematic experimental data are available on the effect of parent austenitic microstructure on deformation processes in shape memory NiTi wires. In this work, we will present and discuss results of systematic thermomechanical loading experiments on nanocrystalline shape memory NiTi wires with grain sizes from 15 to 1000 nm. It will be shown that functional responses of shape memory NiTi wires are controlled by deformation/transformation processes in martensite, which are not yet completely known, probably because they were given less attention than superelastic wires. In view of the current fast development of actuator engineering applications, our results are very useful for optimization of microstructure and functional properties of nanocrystalline actuator NiTi wires.