The adsorption of anions on polycrystalline gold electrodes with and without Cu adatoms in perchloric and sulfuric acid electrolyte solutions was investigated on an electrochemical quartz crystal microbalance in comparison with that on highly ordered Au(111) electrodes. A distinct increase in mass due to the specific adsorption of hydrated bisulfate and perchlorate anions was observed, and their amounts were determined as a function of the potential. It was found that the weight loss in the removal of the Cu adlayer from the Au electrodes was considerably larger than that expected from Faraday’s law in both electrolyte solutions, which was attributed to the co-adsorption of those anions with Cu adatoms. It was demonstrated that the ratio of the number of Cu adatoms to that of adsorbed anions was close to 2 when the coverage of Cu on the Au electrode ranged from 0.2 to 0.5 in both electrolyte solutions.