Mechanical spectroscopy has been used to qualify possible improvements of the mechanical properties of acrylonitrile-butadiene-styrene-carbon nanotubes (ABS-CNTs) composites. The properties of ABS matrix are first investigated. Two relaxations that mark the glass transition of the polybutadiene and the styrene-acrylonitrile (SAN) phases of the polymer are identified. Composite samples with ABS matrix and CNT reinforcement were processed by blending and injection molding. The carbon nanotube additions are 3 wt%, 7 wt% and 15 wt%. The SAN glass transition evidenced by a mechanical loss peak is broadened by the presence of CNT and it is slightly shifted towards higher temperatures. Carbon nanotubes contribute to delay the modulus drop that characterizes the SAN phase glass transition. (C) 2009 Elsevier B.V. All rights reserved.