Topology optimization has been successfully used for improving vibration damping in constrained layer damping structures with viscoelastic materials. Reinforcing carbon nanotubes in a polymer matrix greatly influences the mechanical properties of the polymer. Such nanotube-reinforced polymers (NRP) can be used to further enhance the damping properties of the constrained layer structures. The effects of nanotube inclusions on the damping properties of polymers and applicability of NRP for damping in structures have been studied previously. The inclusion of nanotubes into a polymer matrix provides new design variables in the topology optimization studies on such structures. The aim of this research is to determine the optimal topology and the optimal constituent make-up of the constrained NRP layer, where the volume fraction of the nanotubes in the constrained layer is optimized to maximize the system loss factor.