Reinforcement of natural rubber (NR) was achieved by a novel kind of carbon filler, helical carbon nanofibers (HCNFs). The good interface bonding between HCNFs and NR matrix was confirmed by the analysis of transmission electron microscopy, scanning electron microscopy and dynamic mechanical analyzer. The tensile and dynamic mechanical properties of HCNFs/NR nanocomposites with the filler loading of 1-5phr were studied. When the filler loading is 5phr, HCNFs/NR nanocomposites have a significant enhancement in the modulus at 300% strain (464% and 163% higher than pure NR and N330/NR, respectively), storage modulus (83.5% and 82% higher than pure NR and N330/NR, respectively) at 0 degrees C, with a small decrease in elongation at break. The unique carbon coil structure and abundant surface oxygen-containing functional groups of HCNFs play a critical role in the formation of good interface bonding between HCNFs and NR matrix. This work can provide guidance for the development of HCNFs filled rubber materials with excellent mechanical properties.