The structure and properties of lyocell and viscose rayon fibers are compared in this paper. SAXS results show that the rayon precursor has a higher ratio of larger microvoids, WAXD curves show that both fibers have a monoclinic crystalline structure, but lyocell fibers have higher crystallinity and a larger crystal size. The morphology of lyocell and rayon, observed by scanning electron microscopy (SEM), is the same with an average diameter of 10.6 μm, but different distributions. A Gaussian statistical analysis indicates that the single-strand strength of lyocell fibers is twice as high as for rayon precursors, which have a wider strength distribution. Similar TGA curves show the same pyrolysis mechanism, and based on this, lyocell fibers are proposed as high performance carbon fiber precursors. Lyocell fibers are successfully carbonized under conditions identical to those for manufacturing rayon-based carbon fibers. The two kinds of carbon fibers are compared by SEM and a Weibull statistical analysis.