Zirconia Toughened Alumina (ZTA) Nanocomposites were prepared using Nano sized Zirconia (ZrO2) powders doped with 3% mol of yttria (Y2O3) nanopowders. Diffusion of α-alumina (Al2O3) nanoparticles as well as yttria into the Zirconia lattice network drives monoclinic – tetragonal martensitic transformation. Zirconia toughened alumina (ZTA) composites containing different amount of partially stabilized Zirconia (PSZ) 5, 10, 15 and 20% mol, were prepared via wet mixing and axial pressing. After sintering at different temperatures,1450, 1550 and 1650 °C, phase change in the samples were monitored. X-ray diffraction patterns showed that at constant composition, tetragonal zirconia was increased by temperature increasing due to intensification of diffuse coefficient of alumina and yttria in the system. At constant temperature, remained monoclinic zirconia was increased with Zirconia content increasing.