Spectroscopic investigations of Mn2+ electro-oxidation and MnO2 electro-reduction in acidic media (0.5-2 M H2SO4) have been performed using optically transparent electrodes (OTE). Reticulated vitreous carbon (RVC) has been used as the electrode material. Our results show that in the first step of Mn2+ ions electro-oxidation the unstable in aqueous media Mn3+ ions are formed. In the next step Mn3+ ions can hydrolyse to MnOOH and/or disproportionate to Mn2+ and Mn4+ ions. Contrary to the electro-oxidation of Mn2+ to MnO2, the electro-reduction of MnO2 proceeds in two steps. The first step is strictly connected with electro-generation of MnOOH and the next with regeneration of Mn2+ ions. (C) 2010 Elsevier B.V. All rights reserved.