In this study, particulate nanocomposites with A356 aluminum alloy as a matrix reinforced with 1 and 1.5 wt.% SiCnanoparticles with 50 nm average grain size were fabricated by stir casting method and then the obtained composites were subjected to T6 heat treatment. The mechanical properties such as Hardness Test and Tensile Test of composites Samples were investigated. Microstructures of the samples were also investigated by using optical microscope (OM) and scanning electron microscope (SEM). The results show that T6 heat treated nanocomposites have significantly higher Hardness and tensile Strength compared to the nanocomposites without heat treatment. The enhancement in the mechanical propertiecanis due to the formation of Mg2Si phase and globular silicon particles.Also, increasing in the concentration of SiC nanoparticles led to improve the hardness and tensile strength, So that the highest tensile strength and hardness was obtained for the 1.5 wt.%SiCnanocomposite. Tensile strength and hardness of 1.5 wt% SiCnanocompositesbefore and afterT6 heat treatmentachieved 177MPa and 236MPa and 80 HBN and 123 HBN, respectively.Fracture surfaces were studied using SEM show that failureof all samples is brittle fracture.