ZnO thin films with a thickness of 300 nm were deposited on Si and Al2O3 substrates using electron beam evaporation technique with the aim to be tested as low cost and low power consumption gas sensors for ozone (O3). To characterize the surface roughness and the grain size, which are the main parameters recognized to enhance gas sensitivity since they directly influence the effective sensing area, surface morphology and roughness analyses of the films were performed using scanning electron microscopy and atomic force microscopy, respectively. The crystalline structure and elemental composition were studied through Raman spectroscopy and X-ray photoelectron spectroscopy. Gas tests were conducted at room temperature and zero-bias voltage to assess the sensitivity and response as a function of time of the films to O3 pollutant. The results indicate that the films deposited on Al2O3 exhibit promising characteristics, such as high sensitivity and a very short response time (< 2 s) to the gas concentration. Additionally, it was observed that the films display pronounced degradation effects after a significant exposure to O3.