Motivated by the predicted unusual short Ni-Ni bond length that is comparable to the intermetallic distance anticipated for the triple bond, the nature of Ni-Ni bonding interaction in the triply carbonyl-bridged geometry of the neutral Ni-2(CO)(5) complex has been investigated using a range of state-of-the-art quantum chemistry methods. The elaborate analyses manifest that the tribridged Ni-2(CO)(3) features triple three-center two-electron Ni-C-Ni bonds instead of Ni Ni triple bond. The electron pair donated by the bridging carbonyl ligand should be shared by both nickel centers to achieve the favored (18, 18) configuration.