This study reports on the nanolevel dissolution and polarization behavior of electrodeposited Ru in 0.5 mol L-1 H2SO4 solution with the help of an electrochemical quartz crystal microbalance (EQCM) and inductively coupled plasma-mass spectrometry (ICP-MS) analysis. Results of the cyclic voltammetry showed that during anodic polarization a mass gain at Ru electrode was observed from -0.1 V due to water adsorption and the significant mass gain due to Ru oxide formation was observed from 0.5 V; the start of these processes depended on the potential. ICP-MS analysis of the solution after potential cycling of the Ru electrode showed that only a slight amount of the dissolution occurred when the potential was less than 0.5 V, but the amount of dissolution significantly increased from 0.5 V onward. The potential cycle accelerated the dissolution of Ru. A simple immersion test revealed that the potential of Ru increased until 0.8 V from -0.1 V during the immersion. This shows that the on-off cycle of a polymer electrolyte fuel cell (PEFC) can induce the potential cycle; this will lead to accelerate the dissolution of Ru in the anode catalyst of the PEFC. (C) 2008 The Electrochemical Society.