It is important to elucidate ion-solvent interactions in different solvents not only for electroanalytical chemistry but also for chemistry in general. From this point of view, we have payed attention to two parameters reflecting the ion solvation. One is the complex formation constants (βn) of ions in the proper reference solvents with other complexing solvents, by which the solvating abilities of different solvents can be compared qualitatively with each other. The other parameter is the ionic Gibbs energies of transfer (ΔGOtr) from one solvent to another, by which the solvation energies of ions in different solvent can be compared quantitatively with each other. You can see in Fig.1 a typical example reflecting the differences in the ion-solvent-solvent interactions. The solubility products (Ksp) of AgCl change much differently in the mixtures of water with acetonitrile (AN) and dimethyl sulfoxide (DMSO). This difference in the change of solubility products can be explained well taking into account the change of the ionic Gibbs energies of transfer in these solvent mixtures, as shown in Fig.2. When AN or DMSO is added to water, the silver ion becomes more stable and the chloride ion becomes more unstable in both mixtures. As shown in the Fig.2, relatively speaking, the silver ion becomes stable more rapidly in the water-AN mixtures than in the water-DMSO mixtures. On the other hand, the chloride ion becomes unstable more rapidly in the water-DMSO mixtures than in the water-AN mixtures. This causes the solubility products of AgCl to change much differently in these two solvent mixtures. After all, this is due to the differences in the ion-solvent-solvent interactions, and we tried to evaluate the differences like this on the bases of the ion-solvent complexing and the ionic solvent transfer.