Spectroscopic investigations of Mn2+ electro-oxidation and MnO2 electro-reduction in acidic media (0.5–2M 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.