In this study, Al - MgO composites were produced by powder metallurgy method. In composites, MgO was added as a reinforcement at a rate of 10% by weight, and the average diameter of the reinforcement was <40 nm. The composites are subjected to mixing, compression and sintering time of 5 hours with different sintering temperatures (500 °C – 550 °C – 600 °C). Microstructures of composites were examined by optical microscope and scanning electron microscope (SEM). The theoretical densities of the composites were investigated according to the mixture law and the measured densities according to the Archimedes principle. Porosity content of the composites was determined using theoretical density values and measured density values. The mechanical property of composites was investigated by applying hardness test. Hardness of Al matrix improved dramatically with addition of MgO nano-particles. The maximum hardness value was obtained in AlMgO composite as 104 HB. Grain growth has been shown to inhibit liner growth in hardness. Grain growth occurs in composites with increasing temperature, porosity content decreases and different values are obtained in hardness. The maximum relative density was obtained with sintering temperature of 600 oC.