In the present study, we have investigated the swift heavy ion induced structural modification of ZnO thin film deposited by atom beam sputtering. The films were irradiated by 100 MeV Ag ions at different fluences from 5 x 10(10) ions/cm(2) to 3 x 10(13) ions/cm(2). The influence of the irradiation fluence on structural and optical properties of these thin films was investigated. The structural properties have been studied using X-ray diffraction. The Zn-O bonding was confirmed by Fourier transform infrared spectroscopy and surface morphology was investigated by atomic force microscopy. XRD confirmed that the grain size and texture of the ZnO thin film are increased after the irradiation. The absorption peak intensity corresponding to Zn-O bonding is also increased as a result of energy deposition by swift heavy ion as revealed by FTIR. The AFM study of the films implied that roughness remains almost constant. Power spectral density was also estimated from the AFM micrograph to extract the value of roughness exponent. (C) 2009 Elsevier B.V. All rights reserved.