Thornlike Tb-doped SiC (SiC:Tb) nanostructures were synthesized through a carbothermal reduction of electrospun Tb-doped SiO2 nanofibers (SiO2:Tb). The synthesized SiC nanostructures annealed at a high temperature of 1300 °C displayed a unique morphology and a high crystalline quality with the β-SiC phase. Strong green-light emissions were detected from the SiC:Tb samples. Photoluminescence excitation results show that, besides a small amount of energy coming from the SiC cores (464 nm), most of the energy needed for the excitation of Tb3+ ions comes from the light absorption of the SiO2–Tb surface layers (295 nm) and near-interface regions in the samples (388 nm). Transmission electron microscopy, energy dispersive spectrometry, and Raman analyses suggested that the formations of Tb clusters and SiO2 surface layers are very important to the enhancement of the luminescence behaviors of Tb3+ ions. Finally, we have constructed an excitation model and further proposed an energy transfer mechanism for these thornlike SiC:Tb nanostructures.