Classic denim jeans are generally fabrics having indigo-dyed warp threads. Depending on the desired effect, a bleaching process can be carried out for denim fabrics. Suitable alternatives for oxidative bleaching with sodium hypochlorite and potassium permanganate are not currently available. Some potential alternatives (e.g., peroxide, glucose, and enzymatic bleaching with laccase) are relatively expensive. In this paper, ozonation of denim fabric was investigated as an ecological and practical bleaching alternative. Due to its effective oxidizing potential, denim fabric was treated with ozone; sufficient bleaching results were obtained in a very short time.