The electrochemical processes in dealloying of Au-Sn alloys in a solution of 2 mol dm(-3) HCl have been first investigated in detail by means of in situ potential-dependent and time-resolved Raman spectra. Two clealloying modes were found occurring within different potential regions in the electrooxidation of Au-Sn alloys. One is the mode known as classical dealloying, where Sn is selectively dissolved; and the other a so-called quasi-dealloying mode found here, in which Au re-deposits automatically after simultaneous dissolution with Sn. Meanwhile, nanoporous gold, thin layers of gold nanoparticles stacked on the surface, and colloidal gold in the solution can be prepared from the Au-Sn alloys simply by an electrochemical control of potential. Moreover, the quasi-dealloying manner of Au-Sn alloys has also been grafted onto a pure Au electrode with a tin overlayer by electrodeposition to construct the SERS substrate conveniently. (C) 2008 Elsevier Ltd. All rights reserved.