The gold submicroparticles (AuSMPS) dispersed on indium tin oxide (ITO) substrates were found to be highly active toward CO electrooxidation in solution. The purpose of this paper is to investigate the influence of halide ions on the electrocatalytic activity toward CO oxidation at gold/ITO electrodes. Experimental measurements were based upon constant potential deposition, cyclic voltammetry, scanning electron microscopy, and X-ray photoelectron spectroscopy. it was found that the halide ions exhibited significant poisoning effect on the catalytic activity of AuSMPs/ITO electrodes. The poisoning degree of the three investigated halide ions increases in the order Cl(-) approximate to Br(-) < I(-). The I(-) ion can totally deactivate the AuSMPs/ITO electrode at very low concentrations. whereas the Cl(-) and Br(-) ions can only partially deactivate the AuSMPs/ITO electrode even at high concentrations. The mechanism for the poisoning effect of halide ions on AuSMPs/ITO was discussed on the basis of electrochemical and XPS results. Moreover, we demonstrated an electrochemical method that can be used to effectively desorb the halide ions and reactivate the poisoned AuSMPs/ITO electrodes. (C) 2009 Elsevier B.V. All rights reserved.