Abstract: Nano crystalline zinc oxide (ZnO) films were fabricated by dip coating of ZnO hydrogel. Zinc nitrate hexahydrate and sodium carboxymethyl cellulose were used to prepare the hydrogel. The dip coated samples were annealed at 400°C to obtain the high quality thin films. The films were characterized by X-Ray Diffraction (XRD) which indicated that the films are single phase with the wurtzite structure. Surface morphology of the nanoparticles were studied by Field Emission Secondary Electron Microscopy (FESEM) and optical properties were studied by photo luminescence spectroscopy. Further, gas sensing behaviour were checked for the coated films for ammonia and acetaldehyde vapours at room temperature.