The mechanical and dynamic behaviors of Epoxy/MWCNTs and Epoxy/Al 2 O 3 nanocomposites were investigated in this study. Tensile and impact properties were measured for the two nanocomposites. Free vibration test was applied to measure frequency responses and damping factors. The results showed a reduction in the mechanical properties as well as the damping factors. Frequency response and damping factor was strongly affected by the weight percent of the nanofillers. MWCNTs enhanced the bonding between the Epoxy resin and nanotubes causing reduction in the ability to dissipate energy and improvement in stiffness. The results also demonstrated that, the natural frequency of nanocomposites was increased by increasing the weight percent of nanofillers. The damping factor has the same down trend with the mechanical properties of the nanocomposites.