This paper reports the anomalous infrared spectra of nanometer-sized Fe2O3 particles under certain conditions: some IR absorption peaks obviously shift, theirrelative intensities are changed; all peaks are remarkably broadened; and a broadbackground-absorption band appears. It is suggested that these anomalous IR chac-teristics indicate thata structural phase transition occurs, which results from the polaronic effect due to the increasing of electron-phonon coupling. This effect not only contains the contribution of LO phonons, but also the contribution of softmodes produced by interfacial atoms or molecules.