Topology optimization has been used to maximize the damping performance of constrained damping layer structures with viscoelastic core [1-3]. Studies show that using nanotubes as reinforcements in polymer material might improve the damping and stiffness properties [4,5]. Experimental investigations using nanotube reinforcements in constrained damping layers showed a significant improvement in damping properties of the structure [6]. Optimizing the topology of structures involving nanotube reinforcements can further enhance the damping properties by making optimal use of the nanotubes as reinforcements. In preliminary studies performed with volume fraction of nanotubes as a design variable in the optimization [7,8] substantial improvements in the damping properties were observed. In this work, the topology of a cantilever beam structure involving nanotube reinforced polymer layers is optimized with the objective of maximizing the system loss factor for the first resonance frequency of the base beam. The volume fractions and orientations of the nanotubes in each finite element and the material fraction of the nanotube reinforced polymer (NRP) and the elastic material are the design variables in the optimization process. ABAQUS is used for the finite element modeling and an optimization code NLPQL which uses a sequential quadratic programming algorithm is used for the optimization. Copyright © 2006 by ASME.