The mononuclear [Mn(indH)Cl-2](CH3OH) (indH: 1,3-bis(2'-pyridylimino)-isoindoline) complex has been prepared and characterized by various techniques such as elemental analysis, IR, UV-vis, ESR spectroscopy and X-ray diffraction. The title compound in the presence of a base such as 1-methylimidazole, imidazole or pyridine is efficient catalyst for the disproportionation of H2O2 in CH3CN. Among the various nitrogenous bases investigated in this study imidazole and substituted imidazoles with strong pi-donating ability show better co-catalytic effect. In case of aqueous solution the complex [Mn(indH)Cl-2](CH3OH) shows much higher catalytic activity, and the initial rate of the disproportionation of H2O2 increases with increasing pH and goes through a maximum, which was found at pH similar to 9.6. In this pH value the reaction shows first-order dependence on the catalyst, and saturation kinetics on [H2O2] with V-max = 8.1 x 10(-3) Ms-1, K-M = 489 mm, k(cat) = 38 +/- 2 s(-1) and k(2)(k(cat)/K-M) = 79 +/- 4 M-1 s(-1). (c) 2007 Elsevier B.V. All rights reserved.