A series of three-phase polymer blends, composed of polypropylene (PP) matrix, polyamide-6 (PA6) fillers and polyethylene-octene elastomer grafted with maleic anhydride (POE-g-MA) modifiers, were designed and manufactured. Their mechanical behavior under cyclic loading-unloading was studied by using a video-controlled testing system named as VideoTraction(R) system. It was found that with the increasing PA6 and POE content, the strain hardening became more and more prominent, the volume strain decreased, and the energy dissipated increased. A detailed examination of the cryo-fractured surfaces under SEM was undertaken. The microcavity nucleation, growth and coalescence were observed, and represent the main mechanisms of plastic deformation and damage. The high volume strain comes from the abundant formation of microvoids. On the contrary, the formation of microvoids resulted in relatively smaller quantity of energy dissipation. This result coincides well with the toughening mechanisms of polymer blends revealed by other peoples. (C) 2003 Elsevier Ltd. All rights reserved.