We investigate carbon-based materials (graphite, graphite nanofibers and multi-walled carbon nanotubes) using terahertz time-domain spectroscopy (THz-TDS). The THz-TDS of carbon-based materials has been especially useful for understanding of many fundamental physical properties (e.g. the electronic structure and electron-phonon interactions, etc.) of all sp2 carbons, given that carbon-based materials can be either semiconducting or metallic depending on their geometric structures. A significant difference was obtained in the spectra of graphite nanofibers as compared to the multi-walled carbon nanotubes and graphite.