Nano-alumina particles have excellent mechanical properties. When they are incorporated into metals, they can greatly improve the tensile strength, yield strength, hardness at room temperature and high-temperature properties of the matrix metals. At present, the most widelyused preparation method of nano-alumina in laboratory and industry are liquid phase methods, including precipitation method, sol-gel method, hydrolysis method, micro-emulsion method. Metal matrix composites (MMCs) reinforced by nano-alumina can be produced by ex-situ methods or in-situ methods. Ex-situ method is to add asexisting nano-alumina particles into the metal matrix by powder metallurgy or casting. Ex-situ method is prone to generate agglomeration of the nanoparticles and the interface adhesion between the reinforcement and the matrix may not be very strong. Appropriate processing techniques, such as mechanical alloying and friction stir processing, can mitigate these shortcomings. In-situ method is to synthesize the nano alumina particles during the process through the chemical reaction between oxygencontaining contents with the aluminum matrix, followed by subsequent densification steps such as hot pressing and hot extrusion. MMCs prepared by in-situ methods tend to have better adhesion between the reinforcement phase and the matrix, and the nano-alumina is more uniformly distributed in the matrix. There are two main enhancement mechanisms of nano-alumina in MMCs, one is the Orowan mechanism, the other is some nano-alumina particles are distributed near grain boundaries, which can prevent grain boundary to move. At last, we provide some outlook on the future development of nano-alumina reinforced MMCs and suggest that careful architecture design on the microstructure of the composites may lead to the attainment of composites with superior mechanical properties.