Reaction of ruthenium^(III)-substituted Keggin-type germanotungstate [GeW₁₁O₃₉Ru^III(H₂O)]⁵⁻ (1) with a dimethyl sulfoxide (dmso) produced a dmso-coordinating derivative [GeW₁₁O₃₉Ru^III(dmso)]⁵⁻ (2). Structural characterization of compound 2 by using cyclic voltammetry, UV-Vis spectroscopy, IR spectroscopy, elemental analysis, ¹H-NMR spectroscopy and single crystal structure analysis (monoclinic, P2₁/c, a = 13.461(1), b = 20.198(1), c = 18.078(1), β = 90.426(1), Z = 4) revealed that Ru^III was incorporated in the α-Keggin-type framework and coordinated by dmso through an Ru–S bond. The IR spectra of 1 and 2 were very similar, indicating that 1 also has an α-Keggin structure. Cyclic voltammetry indicated that the incorporated Ru^III-dmso was reversibly reduced to the Ru^II-dmso derivative and oxidized to the Ru^IV-dmso derivative. The redox potential in [α-XW₁₁O₃₉Ru^III/II(dmso)]ⁿ⁻ (X = P, Ge, Si) decreased in the order of P > Ge > Si. Reaction of the complex 2 with ascorbic acid produced a one-electron-reduced compound [α-GeW₁₁O₃₉Ru^II(dmso)]⁶⁻.