The redox behavior of polypyrrole (PPy) film in 0.2 M aqueous KNO3 solution was investigated by cyclic voltammetry (CV) in situ surface-enhanced Raman spectroscopy (SERS). The results show that the Raman intensity of C=C backbone stretching decreases and increases regularly with the anodic and cathodic scans, respectively, owing to the change of surface roughness and the possibility of state transition. The peak position of C-H in-plane deformation remains unchanged both in anodic and cathodic scans. Furthermore, the peak positions of N-H in-plane deformation and ring deformation shift to lower and higher wavenumbers with anodic and cathodic scans, respectively. Also the Raman peak of the NO3- dopant ions appears significant when PPy is in a more oxidized state.