We report on the optical ozone sensitivity of a polyaniline (PANT) film prepared on the inner wall of a polystyrene cuvette by chemical oxidation of aniline from aqueous solution. The PANT film showed changes of optical absorbance in the presence of 50-100 ppm ozone in air at room temperature. The absorbance change was largest at wavelengths in the range of 500-800 nm. The absorbance changes brought about by ozone was partially reversible after removal of ozone from the atmosphere. These results suggest that PANT is a potential material for optical ozone detection.