The dinuclear Ru(II) complexes (arene)Ru(μ-Cl)3RuCl(C2H4)(PCy3) (arene = p-cymene or 1,3,5-C6H3iPr3) react with N2O under mild conditions to give OPCy3 and the trinuclear complexes (arene)Ru(μ-Cl)3Ru(μ-Cl)3Ru(arene). The N-heterocyclic carbene complex (p-cymene)Ru(μ-Cl)3RuCl(C2H4)(IMes) (IMes = 1,3-dimesitylimidazol-2-ylidene), on the other hand, reacts with N2O to give a mixed-valence Ru(II)/Ru(III) complex with a chelating alkoxy ligand. Dinitrogen complexes were identified as intermediates in all reactions. At elevated temperature, the carbene complex (p-cymene)Ru(μ-Cl)3RuCl(C2H4)(IMes) is able to catalyze the oxidation of alcohols with N2O.