Dinuclear d(10) metal complexes such as Pt-2(PH3)(4), PtPd(PH3)(4), and Pd-2(PH3)(4) were theoretically investigated with the ab initio MO method. Size-consistent MP4SDQ and coupled cluster methods yield similar metal-metal bond energy (DE), while the SD-CI method gives the smaller DE value. The DE value decreases in the order Pt(0)-Pt(0) (19) [4.4] > Pt(0)-Pd(0) (16) [4.1] > Pd(0)-Pd(0) (14) [3.8], where the numbers in parentheses and brackets are the DE value (MP4SDQ level; kcal/mol) before and after correction of basis set superposition error (BSSE), respectively. When two PH3 ligands were placed to mimic bis(di-tert-butylphosphino)propane, the DE value of Pt-2(PH3)(4) slightly increases to 22 (13) kcal/mol (MP4SDQ), where the DE value after BSSE correction is given in parentheses. Discussion is presented on basis set effects and correlation effects on DE, electron distribution, and metal-metal bonding nature.