Pt electrode dissolution has been investigated using an electrochemical quartz crystal microbalance (EQCM) in H2O2-containing 0.5 mol dm(-3) H2SO4. The Pt electrode weight-loss of ca. 0.4 mu g cm(-2) is observed during nine potential sweeps between 0.01 and 1.36V vs. RHE. In contrast, the Pt electrode weight-loss is negligible without H2O2 (<0.05 mu g cm(-2)). To support the EQCM results, the weight-decrease amounts of a Pt disk electrode and amounts of Pt dissolved in the solutions were measured after similar successive potential cycles. As a result, these results agreed well with the EQCM results. Furthermore, the H2O2 concentration dependence of the Pt weight-decrease rate was assessed by successive potential steps. These EQCM data indicated that the increase in H2O2 accelerates the Pt dissolution. Based on these results. H2O2 is known to be a major factor contributing to the Pt dissolution. (C) 2011 Elsevier B.V. All rights reserved.