The microstructural changes associated with the tetragonal to monoclinic martensitic transformation at cryogenic temperatures in sintered CeO 2 -ZrO 2 ceramics containing 15.5–16.5 mol% CeO 2 have been studied by means of TEM observations. X-ray diffraction analysis indicates that the stress-induced martensitic phase increases with decreases in both temperature and CeO 2 content. The effects of martensitic morphologies, anti-phase boundaries (APBs) and various dislocation features on mechanical properties are also discussed in the paper.