Polymer nanocomposites consisting of multiwall carbon nanotube (MWCNT) and poly(ethylene 2,6-naphthalate) (PEN) were prepared by a melt blending process in a twin-screw extruder. The storage modulus (G') and loss modulus (G") of the PEN/MWCNT nanocomposites increased with increasing frequency, and this increment being more significant at low frequency. The terminal zone slope of G' for the PEN/MWCNT nanocomposites decreased with increasing MWCNT content, and the nonterminal behavior of those was related to the dominant nanotube-nanotube interactions at higher MWCNT content, leading to the formation of the interconnected or network-like structures of MWCNT in the polymer nanocomposites. The decrease in the slope of the plot of log G' versus log G" for the PEN/MWCNT nanocomposites with increasing MWCNT content suggested the changes in the microstructures of the polymer nanocomposites by incorporating MWCNT. The incorporation of very small quantity of MWCNT significantly improved the mechanical properties of the PEN/MWCNT nanocomposites. (c) 2006 Wiley Periodicals, Inc.