A unique surface-enhanced infrared absorption phenomenon was found and investigated for Ag@polypyrrole nanoparticles. Enhancement of the peak at 1384 cm(-1), corresponding to a C-H bending vibration, gave information on the orientation of the polypyrrole (PPy) molecule in Ag@PPy nanoparticles. It was observed that the contribution of the charge-transfer effect can be amplified with an increased quantity of oxidant FeCl(3) in the polymerization of pyrrole on the Ag core, suggesting that the doped Cl(-) ions in the conductive PPy shell may bring an alteration of the local Fermi level of the Ag nanoparticles and the energy levels in the PPy moleclue, thus achieving an optimal energy matching. These results demonstrated the potential of Ag@PPy nanoparticles as photonics and electronics devices and opened out the applicability of the SEIRA in more-interesting and practical systems.