In this work, we provide the evidence of polymer transcrystallinity in the presence of carbon nanotubes (CNTs). The interfacial morphology of carbon nanotube fiber-polypropylene matrix is investigated by means of polarized optical microscopy (POM), wide-angle X-ray diffraction (WAXD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The supramolecular microstructures of polypropylene transcrystals induced by the nanotube fiber are observed in the range of isothermal crystallization temperatures from 118 degrees C to 132 degrees C. The dynamic process of transcrystallization is analyzed by using the theory of heterogeneous nucleation. Microstructure analysis shows that the nanotubes can nucleate the growth of both alpha- and gamma-transcrystal, and alpha-transcrystals dominate the overall interfacial morphology. Close to the nanotube fiber surface, a cross-hatched lamellar microstructure composed of mother lamellae and daughter lamellae is observed. (C) 2008 Elsevier Ltd. All rights reserved.