Tb-metallofullerenes and single-wall carbon nanotubes (SWNTs) have been selectively synthesized with do arc discharge under 50-200 and 600 Torr helium atmosphere, respectively, by using Tb/Ni/C composite rods as anodes. We propose that only such elements as being able to form acetylides (such as group 11 and III metals and lanthanides) can generate metallofullerenes in high yield and increase the yield of SWNTs produced with transition metal catalysts such as Fe, Co, or Ni. As the yield of the metallofullerenes is inversely proportional to that of SWNTs, these two kinds of fullerene-related materials have similar precursors in the early stage of their growth and have a competitive mechanism in further processes. Based on the high yield synthesis of metallofullerenes, five isomers of Tb@C-82 are produced and four of them are isolated for the first time by multi-stage high-performance liquid chromatography.