Abstarct: In this project nanoparticles of mextastable tetragonal zirconia have been synthesized by dry milling method; wet milling method and precipitation solution method. Experimental results show formation of mextastable tetragonal zirconia with addition 3mol% ytria into zirconia and sintering this powders is possible. Also in this study, synthesis and characterization of the nanocomposites ZrO2-Al2O3, were investigated. The high energy ball milling was used to prepare nanocomposite. The microstructure and phases of the prepared nanocomposites were investigated by using XRD and SEM. The mechanical properties (microhardness) were investigated by Vickers. The results showed that nanocomposites improve mechanical properties. rule of Al2O3 volume percent and different sintering temperature on the mechanical properties has been investigated. In this study by the high energy planetary ball milling decreasing particle size of ZrO2-Al2O3 powders about 30 nm. The result of Vickers microhardness showed that Vickers microhardness of nanocomposite content 90 vol% that was sintered at 1700˚C higher than other nanocomposite.