The　adsorption　behavior　of　uracil.　an　excellent　ligand　in　cyanide-free　silver　plating　on　silver　electrodes　was　studied　with　potential-dependent　surface-enhanced　Raman　spectroscopy　(SERS).　Uracil　was　adsorbed　at　the　silver　surface　with　N3-deprotonated　tautomer　at　pH　10.2,　while　with　N1-　and　N3-deprotonated　tautomers　at　pH　13.6.　Uracil　and　additive　polyethyleneimine　(PEI)　exhibit　a　co-adsorption　behavior　that　holds　the　same　tendency　as　their　adsorption　on　the　silver　surfaces　alone.　The　effect　of　PEI　on　silver　plating　process　is　proposed　from　SERS　and　electrochemical　analysis.　PEI,　acted　as　an　efficient　suppressor　and　grain　refiner　in　this　silver　plating　bath,　was　further　confirmed　by　the　AFM　micrographs.　(C)　2009　Elsevier　B.V.　All　rights　reserved.