Polyacrylonitrile (PAN) fibers containing various concentrations of graphene nanoplatelets (GNPs) were prepared by pressurized gyration, and carbon nanofibers (CNFs) were obtained after subsequent heat treatment and spark plasma sintering (SPS). The influence of processing parameters such as rotational speed, working pressure, carbonization, and SPS temperature on the diameter of the nanofibers has been studied. Furthermore, the thermal properties, morphologies, and crystallization properties of the CNFs have been investigated by using thermogravimetry, scanning and transmission electron microscopy, and Raman spectroscopy. Also, the electrical conductivity and the mechanical properties of these samples have been studied. The results suggest that the gyration conditions and the loading concentration of the GNPs significantly modified the properties of the nanofibers.