The electrochemical reduction processes of Sb(III) on Au electrode were studied by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) electrochemical measurements. The CV analyses reveal that the electrochemical reduction of SbO+ on Au electrode includes three parts: the irreversible reduction of adsorbed SbO+, the reversible underpotential deposition (UPD) of dissociative SbO+, and the irreversible overpotential deposition of dissociative SbO+. Combining the analyses about the redox behaviors of SbO+ as well as the CV measuring results, the reduction of Sb(III) to Sb-0 in the presence of the complex reagent (tartaric acid C4H4O62-) can be conjectured as comprised of four processes: the reduction of adsorbed SbO+ to Sb-0, the UPD of dissociative SbO+, the reduction of absorbed [Sb-2(C4H4O6)](2+) to Sb-0, and the reduction of dissociative [Sb-2(C4H4O6)](2+) to Sb-0. What call also be conjectured by further EIS studies is that the three electrons are not gained simultaneously during the formation of Sb-0 in these four processes. (C) 2008 The Electrochemical Society. [DOI: 10.1149/1.3049349] All rights reserved.