The fabrication of polyethylene-based carbon fibers has been known since late 1970’s and the first patent was issued to Horikiri et al. in 1978. However, this fabrication process has not been further developed into an industrial process due to the complexity of chemical stabilization (sulfonation) and carbonization process. Furthermore, the obtained polyethylene-based carbon fibers possess low tensile strength. Recently, we have successfully developed a new method for the fabrication of high-density polyethylene (HDPE)-based carbon fibers using electron radiation treatment and then carbonization. This developed HDPE-based carbon fibers have similar mechanical properties with the state of the art polyethylene-based carbon fibers but contain a special three-dimensional interconnected microporous structure. Thus, the obtained microporous HDPE-based carbon fibers could be promising candidates as cathodes for lithium-sulfur (Li-S) batteries.