Seven bis-tridentate osmium complexes with Mebib or Mebip (Mebib is the 2-deprotonated form of 1,3-bis(N-methylbenzimidazolyl)benzene and Mebip is bis(N-methylbenzimidazolyl)pyridine) have been prepared, and their electrochemical and spectroscopic properties are compared with ruthenium structural analogues. Among them, four complexes have the [Os(NCN)(NNN)]-type coordination, including [Os(Mebib)(Mebip)](PF6)(2) (1(PF6)(2)), [Os(dpb)(Mebip)](PF6) (2(PF6), dpb is the 2-deprotonated form of 1,3-di(pyrid-2-yl)benzene), [Os(Mebib)(ttpy)](PF6) (3(PF6), ttpy = 4'-tolyl-2,2':6',2 ''-terpyridine), and [Os(dpb)(ttpy)](PF6) (4(PF6)). The other three complexes are [Os(Mebip)(2)](PF6)(2) (5(PF6)(2)), [Os(Mebip)(tPY)](PF6)(2) (6(PF6)(2)) tpy = 2,2':6',2 ''-terpyridine)) and [Os(ttpy)(2)](PF6)(2) (7(PF6)(2)) with the [Os(NNN)(NNN)] -type coordination. Single crystals of 2(PF6) and 6(PF6)(2) have been obtained, and their structures are studied by X-ray crystallographic analysis. The Os(II/III) redox potentials of 1(PF6)(2) to 7(PF6)(2) progressively increase from +0.04, +0.23, +024, +0.36, +0.56, +0.79 to +0.94 V vs Ag/AgCl, which are 200-300 mV less positive relative to the Ru(II/III) potentials of their ruthenium counterparts The highest occupied molecular orbital energy levels of 1(+)-7(2+) are calculated to vary in a descending order. The ruthenium and osmium complexes have singlet metal-to-ligand charge transfer (MLCT) transitions of similar energies and band shapes, while the osmium complexes display additional (MLCT)-M-3 transitions in the lower energy region. Complexes 6(PF6)(2) and 7(PF6)(2) emit weakly at 780 and 740 nm, respectively. Complex 1(PF6)(2) was synthesized as the oxidized Os(III) salt because of the low Os(II/III) potential. The transformation of 1(2+) to 1(+) by chemical reduction or electrolysis led to the emergence of the (MLCT)-M-1 transitions in the visible region.