Herein we consider the role of platinum nanoparticles on water-oxidation catalyzed by manganese oxide. The nanocomposites were synthesized by two different methods and characterized by scanning electron microscopy, energy dispersive spectrometry, high resolution transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and atomic absorption spectroscopy. Then, the water-oxidizing activities of these composites in the presence of cerium(IV) ammonium nitrate as a non-oxo transfer oxidant were studied. We compare these composites with other previously reported Mn oxides and also discuss the important factors influencing the water-oxidizing activities of Mn oxides. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.