Surface-enhanced Raman scattering (SERS) on silver and gold colloid gels formed by a low molecular weight organic gelator, bis-(S-phenylalanine) oxalyl amide, was obtained. Strong Raman signals dominate in the SERS spectra of hydrogels containing silver nanoparticles prepared by citrate and borohydride reduction methods, whereas broad bands of low intensity are detected in the spectra of gold colloid gels. Resemblance between Raman spectrum of the crystalline substance and the SERS spectra of the silver nanoparticle–hydrogel composites implies the electromagnetic nature of the signal enhancement. A change in Raman intensity of the benzene and amide II bands caused by an increase in temperature and concentration indicates that the gelling molecules are strongly attached through the benzene moieties to the metal nanoparticles while participating in gel formation by intermolecular hydrogen bonding between the adjacent oxalyl amide groups. Transmission electron microscopy reveals a dense gel structure in the close vicinity of the enhancing metal particles for both silver colloid gels. Copyright © 2008 John Wiley & Sons, Ltd.