Nanostructured polypyrrole films doped with para-toluene sulfonic acid were prepared by an electrochemical process, and a comparative study of the effects of swift heavy ions and gamma-ray irradiation on the structural and optical properties of the polypyrrole was carried out. Oxygen-ion (energy = 100 MeV, charge state = +7) fluence varied from 1 x 10(10) to 3 x 10(12) ions/cm(2), and the gamma dose varied from 6.8 to 67 Gy. The polymer films were characterized by X-ray diffraction, ultraviolet-visible spectroscopy, and scanning electron microscopy. The X-ray diffraction pattern showed that after irradiation, the crystallinity improved with increasing fluence because of an increase in the crystalline regions dispersed in an amorphous phase. The ultraviolet-visible spectra showed a shift in the absorbance edge toward higher wavelengths, which indicated a significant decrease in the band gap of the polypyrrole film after irradiation. The scanning electron microscopy study showed a systematic change in the surface of the polymer. A similar pattern was observed with the gamma irradiation. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 115:2502-2507, 2010