Composites of polyvinylidene fluoride (PVDF)/carbon nanofibers (CNFs) with different nanofiber contents were prepared by rnelt-blending using a twin-screw extruder by directly mixing CNFs with PVDF in the molten state. Fibers were extruded from the blended pellets. CNFs improved the nucleation efficiency of PVDF but the percent crystallinity decreased with increasing CNF concentration. X-ray crystallinity results showed a change in the alpha phase, but the transition to the beta phase did not occur. Dynamic mechanical analysis (DMA) indicated an improvement in storage modulus and reduced damping factor with increasing CNF concentration. A complementary improvement in mechanical properties was determined from tensile test results. Rheological measurements indicated increased storage modulus, loss modulus, and viscosity values with an increased percentage of CNFs in the PVDF. (c) 2008 Wiley Periodicals, Inc. J Appl Polym Sci 112:254-260, 2009