Department of Chemistry, The University of Burdwan, Burdwan-713 104, India E-mail : barin_1 @yahoo.co.uk Fax : 91-342-530452 Manuscript received 27 August 2001, revised 11 February 2002, accepted 25 April 2002 Eight mixed ligand compounds of osmium(II), -(III), -(IV) of general formula, [Os(dpya)L2]z+ [dpya = 2,2'-dipyridylamine; L = 2-(phenylazo)pyridine (L1), 2-(m-tolylazo)pyridine (L2), 2,2'-bipyridyl (L3), quinolin-8-olate (L4) or 2-methylquinolin-8- olate (L5); �� = 1-3] have been prepared, isolated as their perchlorates. The complexes exhibit several spin-allowed and spin-forbidden charge-transfer transitions in the 200-1000 nm region. In MeCN solutions the chelates display OsIV'-OsIII and OsIII- OsII couples. The stability of metal oxidation levels is discussed in terms of the electrochemical results and correlated to the ��-acceptor properties of these ligands. On the negative side of SCE successive ligand reductions in L1���L3 complexes are observable.