A glassy carbon (GC) electrode was covalently grafted with a layer of sulfanilic acid (SAA) via the formation of amine cation radicals under electro-oxidation. The surface compositions of the resulting electrode were characterized with X-ray photoelectron spectra. The electron transfer of Fe(CN)(6)(3-/4-) to the SAA-modified GC (SAA/GC) electrode in solutions at varied pH was studied with cyclic voltammetry (CV) and analysis of electrochemical impedance. The electrodeposition of gold nanoparticles (AuNP) on the SAA/GC electrode exhibited a dependence on the solution pH, which is attributed to a variation of the terminal charge state of the grafted SAA. The modification of the GC surface with grafted SAA resulted in an enhanced electrodeposition of AuNP. The catalytic activities of AuNP/GC and AuNP/SAA/GC electrodes for reduction of oxygen are compared in phosphate buffer solution with CV. Two distinct reduction features are observed and attributed to a two-step, four-electron reduction of O-2 to H2O through intermediate H2O2. The reduction signals of O-2 on the AuNP/SAA/GC electrode exhibit a shift toward a positive potential, relative to those observed on the AuNP/GC electrode. This indicates that the AuNP on the SAA/GC electrode exhibits an increased catalytic activity for the reduction of oxygen.