Hydrogen gas sensing response of RF sputtered nano-crystalline ZnO thin film is improved by ∼ 34.73 % using swift heavy ion irradiation technique. X-ray diffraction reveals single crystalline wurtzite structure of ZnO thin films. Full width half maximum (FWHM) of (0002) diffraction peak is decreased with increase in ion fluences. However, at very high fluence 1 × 1013 ions/cm2, crystallinity is degraded while FWHM of diffraction peak increases. The ZnO films were grown under highly compressive stress, which was relaxed with incremental ion fluences up to 1 × 1013 ions/cm2. Cathodoluminenscence spectroscopy shows intense predominant peak around ∼ 3.23 eV, which indicates good optical quality of the films. As ion fluence increases, a blue shift appears in near band emission peak from 3.23 to 3.33 eV, which indicates that in-plane stress is decreased. Surface morphology shows generation of self-affine nanostructure and grain fragments as ion fluences were increased. Grain fragmentations had enhanced the surface reaction, and as a result, gas sensor's relative response has improved. It was observed that the gas sensor's sensitivity is strongly dependent on ion fluences and operating temperature. The sensitivity was enhanced from 66.68% to 89.84% with fluence variations from pristine to 1 × 1012 ions/cm2 at 175 °C operating temperature. © 2016 IEEE.