Electrodeposition is one of the most conventional techniques for fabricating alloyed nanofilms. However, given the lack of in situ and real-time techniques in determining the composition and deposition depth of the alloyed nanofilms, effective optimization of alloying effects is difficult, which limits the application of electrodeposition. In the current study, electrochemical (EC) surface plasmon resonance (SPR) was equipped with home-compiled calculation software to achieve the real-time composition and deposition depth profile of the surface-alloyed nanofilms. The results obtained from the Hg-Au alloy proved that EC-SPR is capable of presenting a real-time profile of the alloying process. The in situ and real-time determination will facilitate the effective fabrication of well-controlled alloyed nanofilms and improve the application of the EC method. (C) 2013 Elsevier B.V. All rights reserved.