Mean force potentials [W(r)] for the Na2+-Cl- and Na2+-Na2+ ion-pairs in water are calculated in order to investigate the effects of the cation electric charge on the ion-pair association. The constrained molecular dynamics Simulation method is used. W(r) for Na2+-Cl- shows two minima corresponding to the contact and solvent-separated ion pairs with dissociation-association barriers which are markedly higher than those for Na+-Cl-. Unlike for Na+-Na+, W(r) for Na2+-Na2+ does not show any noticeable minimum.