Nano crystalline tin oxide thin films were deposited on Si and quartz substrates using R. F. magnetron sputtering technique. A set of films was annealed in oxygen environment. These as-deposited and annealed films were irradiated using 100 MeV Ag ions at different fluences ranging from 3×10 11 to 3×10 13 ions/cm 2 . The structural, optical and surface morphological properties of films were studied using X-ray diffraction (XRD), UV-Vis spectroscopy, and atomic force microscopy (AFM) techniques. As deposited films showed the polycrystalline nature and annealing enhances the crystallinity along a particular plane. Upon irradiation at lower fluences up to 3×1012 ions/cm 2 , reduction in crystallinity is observed but at highest fluence 1×10 13 ions/cm 2 a small increase in crystallinity occurs as inferred from XRD spectra. UV-Vis study showed red shift at the lower fluences and blue shift at higher fluences. The pristine film, as observed in AFM micrograph, has randomly distributed surface nano structures with broader size distribution. Irradiation induces the formation of regular shape structures with narrow size distribution. These results may be attributed to the energy deposited by swift heavy ions in the film.