Dynamic mechanical and thermal analysis of aligned vapor grown carbon-nanofibers (VGCNFs)-reinforced high-density polyethylene (HDPE) was performed. High-shear mixing was used to disperse and distribute the nanofibers. Extensional flow was used to obtain anisotropic nanoreinforced composite tapes. Dynamic mechanical analysis showed dual increase of storage modulus and loss modulus with different draw ratios. The modulus and complex viscosities of the drawn samples converged to that of pure PE at high temperatures, indicating that in the melt, the behavior is dominated by the semicrystalline matrix. Additionally, an increase in thermal stability was observed for the composites compared to PE matrix. Differential scanning calorimetry analysis showed that the inclusion of nanofibers hindered the structure evolution of PE upon drawing. © 2006 Elsevier Ltd. All rights reserved.