In this study, aluminum alloy (Al-2wt. % Cu) matrix composites reinforced with 1, 2 and 4 wt. % boron carbide nanoparticles with average size of 80 nm were fabricated via stir casting method at 850 °C. The microstructures of composites were studied by scanning electron microscope (SEM). Density measurement, tensile and compressive tests were carried out to identify the mechanical properties of composites and effect of B4C nanoparticles amount. In all fabricated composites, severe agglomeration was observed in the micrographs. With increasing the amount of B4C nanoparticles up to 2 wt. %, yield and tensile strength increased but with more increasing B4C content they were decreased. Also, the compressive strength of samples was increased with increasing weight percentage of B4C nanoparticles.