Pt dissolution in an H2SO4 solution was investigated in the presence of both H2O2 and Fe2+ using an electrochemical quartz crystal microbalance (EQCM). The EQCM data in the H2O2-containing H2SO4 with and without Fe2+ showed that a remarkable Pt dissolution occurred during the cathodic potential step of 1.36 -> 0.36 V vs. RHE from the 4th cycle, which is further enhanced by the presence of Fe2+. The mass gains and mass losses observed up to the 3rd cycle were also more significant in the presence of Fe2+, suggesting that the roughness of the Pt electrode surface remarkably increased. This phenomenon may be caused by the enhanced O-2 generation due to the significant decomposition of H2O2. As a result, Pt oxidants inducing the cathodic Pt dissolution significantly form from the rearranged Pt atoms, which contribute to the high-rate Pt dissolution in the presence of both H2O2 and Fe2+. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.