An investigation was made on the strain-controlled low cycle fatigue (LCF) of a cast Ni-base superalloy M963 over a wide total strain range of 0.15-0.6% at a temperature range from 700 to 950°C in air. Correlations between dislocation structure and the testing temperature and applied strain amplitude were enabled through transmission electron microscopy (TEM) observation. At a low temperature region (700 and 800°C), dislocation shearing γ precipitates by dislocation pairs and stacking faults at medium and high strain amplitudes, and a well-defined dislocation network at low total strain amplitudes were evident. At a high temperature region (900 and 950°C), dislocations by-passing γ precipitates was the main deformation mode. © 2006 The Japan Institute of Metals.