In this study, gold nanoparticles (AuNPs) with the diameters of maximum 25 nm were self-assembled onto the surfaces of p-aminothiophenol functionalized graphene oxide (ATPGO) sheets simply by mixing their aqueous dispersions. The prepared graphene oxide (GO), ATPGO and AuNPs-ATPGO composites were characterized by a transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), reflection-absorption infrared spectroscopy (RAIRS), the X-ray diffraction (XRD) method and Raman spectroscopy. The electrochemical determination of quercetin (QR) has been studied using square wave voltammetry (SWV) on glassy, carbon electrode (GCE) modified with AuNPs-ATPGO composite (AuNPs-ATPGO/GCE). QR gave rise to a single oxidation peak in the potential interval from 200 to 600 mV in 0.1 M acetate buffer (pH 5.5). The well-defined peaks were observed at the optimized instrumental parameters for SWV such as frequency, amplitude and potential increments. The developed method was validated according to the ICH guideline and found to be linear, sensitive, specific, precise and accurate. The linearity range of QR was 1.0 x 10(-12)-1.0 x 10(-11) M with the detection limit (S/N = 3) of 3.0 x 10(-13) M under optimum conditions. The validated method was applied successfully for the determination of QR in pharmaceutical preparations. (C) 2013 Elsevier B.V. All rights reserved.