Influences of ZrO2 nanoparticles on the mechanical properties and microstructure of hot-pressing Ce-TZP/Al2O3 ceramics were investigated. Meanwhile, t-ZrO2 to m-ZrO2 transformation toughening mechanism was investigated by X-ray diffractometry (XRD) method, and deflection of samples under applied stress were recorded too. The results show that when the percentage of ZrO2 was 20%, the mechanical properties and microstructures of materials are optimum. Moreover, TEM observation show dislocation structures formation both in the Al2O3 and on the grain boundary. Because the dislocation agglomeration and fixation by ZrO2 nanoparticles could deflect cracking or stop cracking development, a strengthening and toughening effect could be achieved. (c) 2005 Springer Science + Business Media, Inc.