The redox behavior in acetone solution of [Ru(NH3)(5)(sulfoxide)](2+/3+) and cis-[Ru(NH3)(4)(dmso)(2)](2+/3+), where linkage isomerizations, (RuS)-S-III-->O and (RuO)-O-II-->S, are brought about by electrochemical oxidation or reduction has been characterized, and the first-order rate constants for them have been obtained. In the isomerization of (RuS)-S-III-->O, a bulky substituent group on the S atom accelerates the reaction over 1000 s(-1) for [Ru(NH3)(5)(sec-butyl sulfoxide)](3+) from 0.4 s(-1) for [RU(NH3)(5)(dmso)](3+). In cis-[Ru(NH3)(4)(dmso)(2)](3+), the rate of the (RuSS)-S-III-->SO is much faster than 1000 s(-1) at room temperature; Substitution on the S atom;barely changes the isomerization rates (similar to 10 s(-1)) for the (RuO)-O-II-->S of the [Ru(NH3)(5)(sulfoxide)](2+) complexes. However, the replacement of a cis ammine by pyridine reduces the rate to 0.7 s(-1). We obtained the related thermodynamic parameters in the dmso, the n-butyl sulfoxide, and the (1,5-dithiacyclooctane 1-oxide)ruthenium complexes and also determined the reaction scheme. The thermodynamics is also presented in for cis-[Ru(NH3)(4)(dmso)(2)](2+/3+).