Both alpha(1)- and alpha(2)-isomers of mono-Ru-substituted Dawson-type heteropolytungstates with a DMSO ligand, [alpha(1)-P2W17O61RuII(DMSO)](8-) and [alpha(2)-P2W17O61RuII(DMSO)](8-), are prepared from the alpha(2)-isomer of a monolacunary derivative, [alpha(2)-P2W17O61](10-). Reaction of [alpha(2)-P2W17O61](10-) with Ru(DMSO)(4)Cl-2 under hydrothermal conditions produces [alpha(2)-P2W17O61RuII(DMSO)](8-) as a main product together with [alpha(1)-P2W17O61RuII(DMSO)](8-), [PW11O39RuII(DMSO)](5-), and [P2W18O62](6-) as byproducts. By addition of KCl to the reaction mixture, K-8[alpha(2)-P2W17O61RuII(DMSO)] is isolated in a moderate yield. On the other hand, reaction of [alpha(2)-P2W17O61](10-) with Ru-2(benzene)(2)Cl-4 under hydrothermal conditions produces an isomeric mixture of [P2W17O61RuIII(H2O)](7-) (alpha(1)-isomer/alpha(2)-isomer ratio: ca. 8/1) as a main product together with [PW11O39RuIII(H2O)](4-) and [P2W18O62](6-) as byproducts. By addition of acetone to the reaction mixture, K-7[P2W17O61RuIII(H2O)] is isolated in a good yield. Reaction of [P2W17O61RuIII(H2O)](7-) with DMSO produces [alpha(1)-P2W17O61RuIII(DMSO)](7-) as a main product and [alpha(2)-P2W17O61RuIII(DMSO)](7-) as a minor product. By addition of KCl and acetone, the alpha(1)-isomer K-8[alpha(1)-P2W17O61RuII(DMSO)] is isolated in a good yield. Both compounds are fully analyzed by CV, NMR (H-1, C-13, P-31, and W-183), IR, UV-vis, elemental analysis, mass spectroscopy, and single-crystal structure analysis. Assuming that isomerization does not occur during the reaction of [P2W17O61RuIII(H2O)](7-) with DMSO, the isolated [P2W17O61RuIII(H2O)](7-) contains the alpha(1)-isomer as a main compound with the alpha(2)-isomer as a minor compound. Unusual transformation of the alpha(2)-isomer of [P2W17O61](10-) to the alpha(1)-isomer occurs. Redox behaviors of [alpha(1)-P2W17O61RuII(DMSO)](8-) and [alpha(2)-P2W17O61RuII(DMSO)](8-) are compared together with Ru(DMSO)-substituted alpha-Keggin-type heteropolytungstates, [alpha-XW11O39Ru(DMSO)](n-) (X = Si, Ge, and P).