The solubiltiy of silver bromate, the Gibbs transfer energy of Ag+ and [FORMULA OMITTED] and the solvent transport number in methanol-dimethyl sulfoxide mixtures are reported. The solubility of silver bromate increases with addition of DMSO. The Gibbs energy of transfer of the silver ion (based on the ferrocene reference method) decreases, while that of the bromate ion becomes slightly negative with the addition of DMSO. The solvent transport number Δ passes through a maximum (Δ = 1.0 at XDMSO = 0.65. From these results, it is concluded that the silver ion is preferentially solvated by DMSO whereas the bromate ion shows no preferential solvation. © 1984, Walter de Gruyter. All rights reserved.