Tin oxide thin films were deposited on well cleaned glass substrates by thermal evaporation in vacuum and were annealed at 500 °C in the open atmosphere inside a furnace for 90 min for promoting the sensitivity of the films. The X-ray diraction studies revealed that the as-deposited films were amorphous in nature and the annealed films showed appreciable crystalline behavior. The annealed thin films were then irradiated using ⁶⁰Co gamma source. The radiation induced changes were then studied by X-ray diraction, scanning electron microscopy, UV-vis spectroscopy and I-V characterization. The remarkable increase in the average grain size, the decrement in the energy band gap and resistivity due to the gamma irradiations up to a certain dose and the reversal of these properties at higher doses are the important observations. The large changes in the conductivity and energy band gap of the annealed thin films due to gamma irradiation make these films quite important device material for the fabrication of gamma sensors and dosimeters.