Dynamic mechanical and morphological properties of the polycarbonate (PC)/multi-walled carbon nanotube (MWNT) composites were studied by dynamic mechanical thermal analysis (DMTA) and X-ray diffractometry, respectively. For the without annealed PC/MWNT composites containing the higher content of the MWNT (>= 7.0 wt%), double tan delta peaks were observed, which could be explained by the phase separation morphology model. For the annealed PC/MWNT composites, a broad single tan 5 peak was observed. From the X-ray diffraction of the annealed PC/MWNT composites, it was observed that more regular structure of the PC was obtained, which was consistent with the result of the thermal analysis of the annealed PC/MWNT composites. From the dynamic mechanical properties, thermal analysis, and X-ray diffraction of the annealed PC/MWNT composites, it is suggested that PC/MWNT composites show a broad single tan delta peak and partially crystalline structure of the PC in the PC/MWNT composites by annealing. (c) 2005 Elsevier Ltd. All rights reserved.