The present work includes the study of the dynamic properties of the nanocomposites specimens. The dynamic properties of A356/Al 2 O 3 nanocomposites were investigated through different fabrication conditions. The A356/Al 2 O 3 nanocomposites specimens were fabricated using a combination between the rheocasting and squeeze casting routes. The composites were reinforced with Al 2 O 3 particulates of 60 and 200 nm and different volume fractions up to 5 vol%. The dynamic properties of the A356/Al 2 O 3 nanocomposites were investigated through measuring the dynamic properties of specimens. Free vibration method is used to measure frequency response (f n ), and damping factor (ξ). The viscoelastic properties such as loss factor η, storage modulus (E'), and loss modulus (E") were obtained. The results concluded that, the dynamic properties of nanocomposites were improved by increasing the volume fractions of nanoparticulates and decreasing the nanoparticulates size. The results indicated also that, the damping factor, and the related parameters (η, E' and E") was strongly affected by increasing both volume fraction and the particulates.