Ce-TZP/Al2O3 nanocomposites were prepared from mixture of self-made Ce-TZP nanometer powder and commercial Al2O3 powder by hot-pressing method. Influences of nanometer ZrO2 particles on the mechanical properties and microstructure of Ce-TZP/Al2O3 ceramics were investigated. Meanwhile, t→m 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 were preferential. Additionally, TEM observation show that dislocation structures form both in the Al2O3 grain and on the Al2O3grain boundary.