Indium oxide (In2O3) thin films have been prepared by sol-gel and RF sputtering techniques. The sol-gel film appeared to be much more sensitive to ozone compared to the RF sputtered film. The morphology of both films was examined by SEM, while their chemical composition was analyzed using X-ray photoelectron spectroscopy (XPS) in order to understand the properties responsible for the high sensitivity of sol-gel films. The examination results showed that the sol-gel films are very porous and uniform in grain size, but the RF films are relatively dense and of coalescent grains. XPS analysis also highlighted that there may be oxygen vacancies on the surface of sol-gel films. The large surface areas of sol-gel films and oxygen deficiency in the film structure are responsible for its higher sensitivity.