Adsorption of isonicotinic acid onto a silver colloidal particle surface was investigated over a wide range of solution pH by surface-enhanced Raman scattering. The molecule was found to adsorb onto the surface as an anionic form with the carboxylate-to-metal coordination providing the major interaction for the adsorption. The nitrogen-to-metal coordination seemed to play a secondary role in the adsorption process. Unlike the cases in organometallic chemistry, the flat coordination of the carboxylate group to the silver surface via its π orbitals was observed for isonicotinate adsorbed onto the aqueous sol particle surface. The adsorbate structure was found, however, to be completely different from that of the silver isonicotinate salt. That is, in the salt state, the carboxyl group was not coordinated at all to silver in contrast with the isonicotinate which was adsorbed onto the silver surface. Instead, the silver cation was bound to two ring nitrogen atoms.