In this study the ozonation effect on the biologically treated opium alkaloid wastewater was examined. The ozonation studies were performed 0 to 50 minutes at three different pH values. According to the results, while low COD and TOC removal efficiencies could be supplied, very high color removal efficiency could be achieved by ozonation. The best removal efficiencies of COD, TOC and color were obtained at low pH values because of high alkalinity. The biological treatability can be increased by the partial ozonation as an indication of increasing BOD.