We report the synthesis and structure determination of a new Au-20 nanocluster coordinated by four tripodal tetraphosphine (PP3) ligands {PP3 = tris[2-(diphenylphosphino)ethyl]phosphine}. Single-crystal X-ray crystallography and electrospray ionization mass spectrometry show that the cluster assembly can be formulated as [Au-20(PP3)(4)]Cl-4. The Au-20 cluster consists of an icosahedral Au-13 core and a seven-Au-atom partial outer shell arranged in a local C-3 symmetry. One PP3 ligand coordinates to four Au atoms in the outer shell, while the other three PP3 ligands coordinate to one Au atom from the outer shell and three Au atoms from the surface of the Au-13 core, giving rise to an overall chiral 16-electron Au cluster core with C-3 symmetry.