The electrochemical redox mechanism of I(-) ion under different concentrations on gold electrodes was studied in detail using the EQCM technique (a combination of the QCM technique and cyclic voltammetry). The redox behavior of the I(-) ion on a gold microelectrode when no supporting electrolyte was added was compared with a conventional gold microelectrode. Due to the small current and the very low solution iR drop of the microelectrode, the actual oxidation potential of I(-) on the microelectrode was much more negative than that of the conventional electrode and its anodic peak was better defined. Therefore the gold microelectode was employed for the determination of I(-). A linear range of 1.0x10(-5)-0.1 mol l(-1) with a detection limit of 1.0x10(-6) mol l(-1) was obtained on the microelectrode in pure KI aqueous solution. Two samples were measured using this method and the results were in good agreement with those indicated or calculated..