Thin films of indium oxide grown on quartz substrates were subjected to 100 MeV Ag 9+ and O 7+ ions irradiation. The pristine and swift heavy ions irradiated films were characterized using X-ray Diffraction, Rutherford Backscattering Spectrometry, Scanning Electron Microscopy and UV-Vis Spectroscopy to examine the effect of irradiation with ions having large difference in the values of electronic energy loss (Se) on the structural, microstructural and optical properties of indium oxide thin films. XRD and SEM studies revealed deterioration in crystallinity along with decrease in both crystallite size and grain size upon irradiation with both Ag 9+ and O 7+ ions. However, the decrease in the crystallite size and grain size in comparison to the pristine film was more radical for irradiation with Ag 9+ ions. RBS spectra suggest that the electronic sputtering in the indium oxide films due to SHI irradiation is very less. AFM images illustrate the decrease in surface roughness from 29.8 nm for the pristine film to to 27.4 nm and 26.7 nm on irradiation with 100 MeV O 7+ and Ag 9+ ions at a fluence of 3.3×10 13 ions/cm 2 . Also, UV-Vis study revealed an increment in the value of optical band gap from 3.41 eV for the pristine film to 3.53 and 3.67 eV for indium oxide films irradiated with of 3.3×10 13 ions/cm 2 fluence of O 7+ and Ag 9+ ions respectively. The irradiation induced structural and optical modifications have been explained using the Thermal spike model. Along with the structural and optical properties, sensing properties of the pristine and irradiated films for 100 ppm methane gas at an operating temperature of 300 o C have also been examined and the results have been correlated with the induced structural modifications.