A new diMnIII complex, [Mn2L(OAc)2(H2O)](BPh4)·3H2O (1), obtained with the unsymmetrical N3O3-ligand H3L = 1-[N-(2-pyridylmethyl),N-(2-hydroxybenzyl)amino]-3-[N'-(2-hydroxybenzyl),N'-(benzyl)amino]propan-2-ol, has been prepared and characterized. The unsymmetrical hexadentate ligand L3- leads to coordination dissymmetry (dissimilar donor atoms) around each Mn ion (N2O4 and NO4(solvent), respectively) leaving one labile site on one of the two Mn ions that facilitates interaction of the metal center with H2O2, as in Mn catalase. 1 is able to catalyze H2O2 disproportionation in acetonitrile, with second-order rate constant kcat = 23.9(2) M-1 s-1. The accessibility of the MnII2 state and the closeness of the two one-electron reduction processes suggest 1 employs MnIII2/MnII2 oxidation states for catalysis.