Electrochemical surface-enhanced Raman spectroscopy (EC-SERS), combined with cyclic voltammetry, and the density functional theoretical (DFT) method were used to investigate self-assembled monolayer (SAM) adsorption and reduction processes. Here, we choose the system of interest, being thiolacetyl-terminated 2-phenylene ethynylene-substituted anthraquinone molecule (2-AQ) on gold electrodes in buffered aqueous and aprotic solutions. In the buffered aqueous solution, the results of cyclic voltammetry and EC-SERS measurements, as well as DFT calculations, indicate that the adsorbed molecules pass through a two-electron two-proton reduction reaction with cathodic polarization. In particular, the latter two methods confirmed the structural changes of SAMs during the process of redox reaction, 2-AQ + 2e + 2H+ → 2-AQH2, where 2-AQ and 2-AQH2 are the oxidized and reduced forms, respectively. In aprotic solutions (acetonitile), a stepwise reaction mechanism was proposed on the basis of the results of EC-SERS and DFT calculations. The first reduction peak should be a half reaction process 2-AQ + e → 2-AQ−, where 2-AQ− is a single electron reduced form. Compared with that of 2-AQ SAMs in the buffered aqueous solution, the results of EC-SERS and DFT calculations in aprotic solution suggested that the solvent effect significantly influences the redox process of 2-AQ in electrochemical interfaces. Copyright © 2012 John Wiley & Sons, Ltd.