YRh4B4, which exhibits high- superconductivity in the RRh4B4 system, has two types of crystal structures, CeCo4B4 type (pt-type) and LuRu4B4 type (bct-type). Both types of structure have similar (pt-type; = 10.6 K, bct-type; = 9.8 K), but the of both compounds is very different, pt-type; = 2.50 T and bct-type; = 9.85 T. From our results, one can see that the difference in between pt-YRh4B4 and bct-YRh4B4 is mainly caused from the difference of the density of state at Fermi energy. The high- in pt-YRh4B4 is derived from the high Debye temperature caused by vibrations of boron. In contrast, in bct-YRh4B4 it is caused by a stronger electron–phonon coupling than in pt-YRh4B4. Regarding the symmetry of superconductivity, it is suggested that pt-YRh4B4 is a clean limit superconductor and has basically a fully gapped superconducting gap, but is slightly anisotropic from the results of ) below and . However, bct-YRh4B4 is a dirty limit superconductor and has an anisotropic superconducting gap from the results of below and .