Cysteine, an important amino acid, is an often-used self-assembly regent in the preparation of modified electrodes and biosensors. However, our understanding of the cysteine self-assembly process on gold surface is still not well understood. In this study, the electrochemical behavior of modified electrodes based on Cys self-assembly on gold surface was investigated. The cyclic voltammogram shows a pair of well-shaped redox peaks (0.14 V of anodic peak and -0.02 V of cathodic peak) at this modified electrode in phosphate buffer solution (pH 7.0). The electrochemical properties of the couple redox peaks were investigated systematically by cyclic voltammetry. The experiment results indicate that hydrous gold(I) oxide on the interfacial of the modified electrode exhibited good electrocatalytic activity of ascorbic acid oxidation. The formation mechanism of hydrous gold(I) oxide is also discussed. This oxide can participate in electrocatalytic processes as mediator to improve electrochemical oxidation of ascorbic acid. (C) 2012 Elsevier B.V. All rights reserved.