By using ab-initio calculations, the adsorption and diffusion properties of charged Au dimers (Au-2(+) and Au-2(0)) on MgO(100) were investigated and compared with those of the charge-neutral dimer (Au-2(0)). The most favored adsorption structure of Au-2(+) on MgO(100) is the upright dimer on a surface O atom in agreement with that of Au-2(0). The surface diffusion of Au-2(+) on MgO(100) occurs by the leapfrog process with a barrier height of 0.38 eV lower than that of Au-2(0) (0.66 eV). The most stable adsorption structure of Au-2(0) on MgO(100) is the flat-lying dimer on two surface Mg atoms. The surface diffusion of Au-2(0) on MgO(100) can proceed by the hopping and walking processes with a barrier height in the range of 0.05?0.11 eV, which is much lower than the diffusion barriers of Au-2(+) and Au-2(0). Furthermore, detailed information on the electronic properties of Au-2(0), Au-2(+), and Au-2(0) are also presented.