Relatively poor creep resistance is considered as a deficiency of thermoplastics in general. Our previous study [I] on the enhanced creep resistance of polyamide 66 by a very low filler content of spherical nanoparticles explored an exciting phenomenon, which is expected to be able to promote the engineering applications of these materials. In order to comprehensively and deeply understand the effect of nanoparticles, here we provide a systematic investigation on various kinds of nanofillers, i.e. spherical particles and nanoclay, modified polyamide 66 under different stress levels (20, 30 and 40 MPa) at room and elevated temperatures (23, 50 and 80 degrees C), respectively. Static tensile tests are also performed at corresponding temperatures. Creep was characterized by considering the isochronous stress-strain curves. creep rate. and creep compliance with influence of temperature and stress, respectively. It was found that the creep resistance of nanocomposites was significantly enhanced by nanoparticles without sacrificing the tensile properties. The orientational hardening. as well as the thermal and stress activated process are briefly introduced in order to understand the mechanisms of viscoelasticity of these nanocomposites. (c) 2006 Elsevier Ltd. All rights reserved.