This work showed that chemically-synthesized gold nanoparticles, AuNPs, supported onto a Si (111) wafer electrode, can be selectively modified with a copper adlayer through underpotential deposition (upd) conditions, using both: potentiodynamic or potentiostatic electrochemical means. From analysis of experimental potentiostatic current density transients, it is shown that Cu upd onto the AuNPs occurs by a mechanism involving the simultaneous presence of a Langmuir-type adsorption-desorption and an instantaneous two-dimensional, 2D, nucleation process. The influence of the applied potential on the Cu upd kinetics and on the extent of Cu atoms coverage over the AuNPs was also reported. Furthermore, it is shown that the Cu overpotential deposition, opd, onto these AuNPs, starting from a potential in the upd region where the AuNPs surface is free from Cu atoms, occurs through a 2D-3D mechanism, where the 3D nucleation is mass-transfer controlled. Notwithstanding, when Cu opd started at the equilibrium potential the mechanism solely involved 3D nucleation. (C) 2017 Elsevier B.V. All rights reserved.