Polyvinyl alcohol (PVA)-protected Ag colloids were prepared by an electrolysis method. The surface enhanced Raman scattering (SERS) spectra of Methyl Orange (MO), one of the Azo-dye molecules, in Ag colloids were successfully recorded with good concordance comparing to the theoretical results calculated by the Gaussian'98 program. The MO was adsorbed on the surface of Ag nanoparticles by trans-form which plays an important role for the SERS effect. However, the SERS spectra of MO in Ag colloids prepared by chemical reduction method did not appear which may be because of the competition of the borate or citrate ions with the MO. In order to test the applicability of these colloids, the SERS spectra of Sudan red (III) (SR), another of Azo-dye molecules, were measured and the result was good. Crown Copyright (C) 2009 Published by Elsevier B.V. All rights reserved.