Three new nitro-nitrito isomeric pairs are prepared and characterized as cis-[Ru(NO)X(2,2’-bpy)(2)](2+), Cis-[Ru-(NO)X(ppca)(2)], and cis-[Ru(NO)X(2,2’-bpy)(py)(2)](2+) (X = ONO, NO2; 2,2’-bpy = 2,2’-bipyridine; pyca = pyridine-2-carboxylate; py = pyridine). Molecular structures of the isomers are established by X-ray structure studies, except for cis-[Ru(NO)(ONO) (pyca)(2)]. Redox-induced linkage isomerization occurs in cis-[Ru(NO)X(2,2’-bpy)-py)(2)](2+) (X = ONO, NO2); the nitrito isomer is capable of being interchanged to the nitro isomer, via a one-electron redox process of the (RuNO)(3+) moiety. Thermally-induced isomerization also occurs, with different isomerization patterns, depending on the spectator ligands : cis-[Ru(NO)X(2,2’-bpy)(2)](2+) gave an equilibrium mixture of the nitro and the nitrito isomers; in cis-[Ru(NO)X(pyca)(2)], the nitrito isomer changed to the nitro isomer; contrastively, the nitro isomer of cis-[Ru(NO)X(2,2’-bpy) (py)(2)](2+) converted to the nitrito isomer. Some mechanistic investigations about the isomerization reactions were carried out using various N-15-substituted complexes; no oxygen exchange reaction between the nitrosyl and the nitro (nitrito) ligands was found.