Abstarct: Engineering ceramics have high stiffness, excellent thermostability, and relatively low density, but their brittleness impedes their use as structural materials. Among alumina as a ceramic engineer despite having unique Features such as high hardness, high wear resistance, high fatigue and corrosion resistance, has low toughness. Incorporating carbon nanotubes (CNTs) into a brittle ceramic might be expected to provide CNT-ceramic composites with both high toughness and high temperature stability. Another effective method to improve the toughness of alumina, is using of the tetragonal zirconia as a secondary phase. At first aluminum nitrate aluminum nitrate is dissolved in ethanol. Also multi wall-carbon nanotubes (MWNTs) are dispersed into deionized water. Then aluminum nitrate solution is added dropwise into dispersed MWNTs and heated on stirrer to dried completly. Heating the material at 400 °C leads to make aluminum oxide coating on the MWNTs. The obtained powder is mixed with alumina and zirconia (3YSZ) powder and formed into cylindrical pellets using uniaxial pressing. To study the effect of aluminum oxide particle size on the mechanical properties, the same weight percent of nano and macro alumina added to the nanocomposition, separately. Sintering of the specimens is done in a tube furnace under argon atmosphere at 1300 °C for densification. Densities of sintered specimens are measured using Archimedes’ method with water as the immersing medium. The fracture strength was measured by ball on three balls method and the fracture toughness and microhardness of the samples were studied by Vickers microhardness test. It was shown that alumina coated on the MWNTs and crystal structure of MWNTC obtained by sintering at 1300 °C .In addition, it was found that by adding MWNT with 3 wt% to ZTA ceramic composites hardness and fracture toughness.improved Furthermore, added nanoalumina to the nanocomposite compared to the larger particles of alumina increased fracture strength and hardness and leads to reduced density of the nanocomposite.