Surface-enhanced Raman scattering (SERS)active substrates with high enhancement were prepared by an in situ reduction method. Novel silver/poly(vinyl alcohol) (PVA) nanocomposite films were obtained, in which the silver nitrate, poly(gamma-glutamic acid) (PGA), and PVA acted as precursor, stabilizer, and polyol reducant, respectively. The UV-visible spectra of the as-fabricated films showed that the surface plasmon resonance (SPR) absorption band was narrow and of a stronger intensity, which indicates that the Ag nanoparticle size distribution on the substrate was highly uniform. This finding was further confirmed by X-ray diffraction (XRD), transmission electron microscopy (TEM), and field-emission scanning electron microscope (FE-SEM) measurements. It was found that a PGA-stabilized PVA nanocomposite film revealed the presence of well-dispersed spherical silver nanoparticles with an average diameter of 90 nm. The new substrate presents high SERS enhancement and the enhanced factor is estimated to be 10(6) for the detection of benzoic acid.