The dependence of intensity of surface enhanced Raman scattering on the concentration of poly(4-vinyl pyridine) solutions was investigated. The spectral quality and the Raman scattering intensities of the enhanced spectra of poly(4-vinyl pyridine) adsorbed on nitric acid-roughened silver foil were inversely proportional to the concentration when it changed from semi-dilute to very dilute. The band intensity-concentration plot displays a turning point corresponding to the critical concentration for coil shrinkage. The observed phenomena are in accordance with Qian’s proposal for the existence of C(s) for coil shrinkage in dilute solution.