This paper investigates the effect of mechanical pre-strain on interfacial friction damping in nanotube polymer composites. Oxidized single-walled carbon nanotubes were dispersed in a polycarbonate matrix using a solution mixing technique. To characterize the damping response, the material storage and loss modulus was measured by application of dynamic (sinusoidal) load to the nanocomposite in the uniaxial direction. A static pre-strain (in 0.35-0.85% range) was then superimposed on the dynamic strain to quantify its effect on the material response. The results indicate that application of pre-strain facilitates the activation of interfacial slip at the nanotube-polymer interfaces at relatively low dynamic strain amplitudes. This is because pre-strain raises the interfacial shear stress for the nanotube inclusions allowing the critical stress for tube-matrix interfacial slip to be reached at lower strain amplitudes. In this way pre-strain significantly improves the effectiveness of the nanotube-matrix sliding energy dissipation mechanism for damping enhancement in composite structures.