Abstract: In order to improve the performance and prolong the life of shape memory alloy materials (SMA), it is very important to trace and study the microstructure change during the fatigue of SMA. The microstructure features between samples before and after thermal fatigue (about 100,000 thermal cycles) of NiTi-SMA film was examined and compared with each other by transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS). It was found that there is no difference in microstructure between the two kinds of samples except some precipitates appeared in the fatigue specimen. These precipitates which may be identified as TiNi₃ phase with a grain size of 10-20 nm may impede the transformation from martensite to austenite which is the working mechanism of SMA during thermal cycling. Therefore, these precipitates result in the serious decay of SMA performance and further fracture of the SMA material.