This study concerns with the reduction of the COD and deceleration of dyeing wastewater from DAEGU city area by ozonation. The COD reduction by ozonation follows near linear relationships versus ozonation time, temperature and concentration. The color in dyeing wastewater and of dyes can he strikingly reduced as the water is quasi colorless after ozone treatment. COD reduction rate of wastewater was found not to be dependented on pH, however, high temperature gave better results, although economically not feasible. The ozonation of dyeing wastewater can give good results when dyes, scouring agent and sticking agents were pre-separated.