Aluminium based metal matrix composites produced by powder metallurgy are used in the aerospace and automobile industries because of their high strength, light weight, etc. The properties may become much better when nanosized reinforcements are used. In this research, the morphological, microstructural and mechanical properties changes during nanosized alumina increment to Al powder were studied. Because nanosized particles are extremely prone to agglomeration, all of the samples have been milled for 12?h by a planetary ball mill. The process was conducted for Al?(0?20)?wt?%Al2O3 powders to explore the role of reinforcement nanoparticles on the microstructure and mechanical properties. The results showed that the strength, ductility and hardness were increased by increasing the reinforcement nanoparticles weight percentage. Also, addition of hard particles accelerated the milling process, leading to faster work hardening rate and fracture of the aluminium powder.