New 4d-4f heterometallic complexes with a one-dimensional structure, (1)∞[{Ru(valen)(CN)2KRu(valen)(CN)2}{Ln(O2NO)2(CH3OH)3}]·2CH3OH (Ln = Gd, Tb, Dy), have been assembled from the reaction of [K(H2O)2Ru(III)(valen)(CN)2]·H2O with lanthanide nitrates. The exchange interaction between Ru(III) and Gd(III) mediated by the cyanido ligand was determined for the first time and found to be weak and of antiferromagnetic nature.