The anodic dissolution process of a Au(111) oriented electrode in HC10(4) solution containing various concentrations of chloride ion was investigated using an electrochemical quartz crystal microbalance (EQCM) under potential sweep and potentiostatic conditions. The in situ EQCM results clearly demonstrated that gold dissolves through a 3e(-) oxidation process in the anodic potential region. No evidence for the 1e(-) dissolution was obtained in the present study.