Neurofilaments (NFs) are composed of neurofilament triplet proteins (NFTPs), NF-L, NF-M and NF-H. The structure of neurofilaments, isolated from bovine spinal cords, was studied with scanning tunneling microscope (STM). STM images of NFs with relatively higher resolution were obtained for the first time. The results showed that NFs revealed as a kind of periodic structure, composed of a long core filament (9–11 nm in diameter) and lateral sidearms projecting from the core filament every 10 nm space. There were undulant structures on the surface of core filament. The periodicity along the core filament was obtained from cross-section analysis. The periods along the axis and two sides of the core filament were uniform to be about 10 nm. In some regions, there was also 20 nm periodicity, indicating the distance between two adjacent long sidearms in the topography, which coincided with the periodic distribution of sidearms observed by metal shadowing electron microscopy. However, the previous half-staggered model could not explain the 10-nm periodicity. According to the results from STM experiments, it could be deduced that three-quarter-staggered organization of subunits must take place during the assembly of native NFs.