Abstract <p>The stability constants of cadmium(II) complexes with the glycylglycine anion in aqueous dimethyl sulfoxide solutions were determined by potentiometric titration at 298 K and an ionic strength of solutions of 0.1 M. The stability of cadmium(II) glycylglycinates increased at increased concentrations of dimethyl sulfoxide in solution. Using our own and literature data, the Gibbs energies of the transfer of cadmium(II) glycylglycinate complexes from water to the water–dimethyl sulfoxide solvent were calculated, and the contribution of reagent resolvation to the change in the Gibbs energy of the reaction of formation of complex particles was considered. The increased stability of the cadmium(II) glycylglycinate complex in aqueous dimethyl sulfoxide solutions is mainly determined by the weakening of the solvation state of the ligand.</p>