Surface enhanced Raman scattering (SERS) technique was used to observe the adsorption structure of serotonin (5-hydroxytryptamine, 5-HT) monolayers formed on silver electrode surface at pH 11 and also by the aid of density functional theory (OFT). The SERS spectrum implied that monolayers of 5-HT could be self-assembled on the silver surface through O-10 and N-6 atoms and the molecular plane should be tilted on the surface. In situ electrochemical SERS experiment was performed in 0.1 mol L-1 KCl solution to investigate the stability of the 5-HT monolayers on the silver electrode surface. It could be found that 5-HT monolayers on silver surface experienced the changes of adsorption fashions as the potential shifting to a more negative direction prior to complete detachment from the silver surface. (C) 2012 Elsevier B.V. All rights reserved.