Use of carbon nanotubes as additives to composite parts for the purpose of increased damping has been the subject of much recent attention, owing to their large surface area per weight ratio which provides for frictional losses at the carbon nanotube-resin matrix interface. This article presents an experimental study to quantify the structural damping in composites due to the addition of carbon nanotubes to thermosetting resin systems with and without fiberglass reinforcement. Carbon nanotubes of varying quantity and morphology are ultrasonically dispersed in epoxy resin and are compression molded to form test samples that are used in forced vibration, free vibration with initial tip deflection, and tension tests to determine their damping ratio, specific damping capacity, and Young's modulus. Results show increased stiffness and specific damping capacity with the addition of carbon nanotubes and particularly increased frictional loss with increasing surface area to weight ratio. The addition of fiberglass reinforcement to composite samples is shown to reduce the effective damping ratio over plain epoxy samples and carbon nanotube-filled epoxy samples.