The adsorption of (3-mercaptopropyl)trimethoxysilane (MPS) has been studied on iodine coated gold electrodes. The MPS adsorption from alcoholic solution on Au(I 11) and iodine coated Au(I 11) was studied by atomic force microscopy (AFM) and Xray photoelectron spectroscopy (XPS). The electrochemical formation of MPS monolayers was studied by cyclic voltammetry on polycrystalline uncoated and coated gold electrodes with different MPS pre-treatment conditions. Lead electrochemical deposition was used to probe the defect sites of the surfaces created. The MPS-over-iodine coated gold surface produces a lower-density monolayer than the MPS over pure gold. The MPS monolayer formed electrochemically on the iodine coated gold is chemically equal to its counterpart after the iodine desorption. The MPS adsorption occurs via an Au-S bond, after the partial reductive-desorption of the iodine monolayer from the iodine coated gold electrode, and produces an ordered composite monolayer of MPS/iodine. The size of the defects can be controlled by varying the electrochemical preparation conditions, using the following reaction: Au-I-(ads) + MPS-H-(ac) + e(-) <----> Au-MPS(ads) + H-(acs)(+) + I-(ac)(-).