We have synthesized a mononuclear ruthenium(II) azido complex (1) and a dinuclear ruthenium(II) mu-azido complex (2) having N,N-bis(2-pyridylmethyl)-N-bis(2-pyridyl)methylamine (N4Py) as a pentadentate ancillary ligand. In the crystal structure of 2, intramolecular pi-pi stacking was found between the pyridine rings of the two different N4Py ligands, contributing to stabilize the dinuclear mu-azido structure. pi donation from the HOMO pi* orbital of the mu-azido ligand to the Ru-N(pyr) bond increases the bond order between the terminal and central N atoms in the mu-azido ligand to strengthen the N-N bonds of the mu-azido ligand. The mu-azido complex 2 was revealed to exhibit a stepwise oxidation behavior in CH3CN to afford a Ru-II-mu-azido-Ru-III mixed-valence (MV) state upon one-electron oxidation. The MV state of one-electron-oxidized 2 was categorized in the Robin-Day class II with the electronic coupling constant (H-ab) of 570 cm(-1).