Abstract This paper examined the possibility of applying ozone (O3) and O3 combined with ultraviolet (UV) to degrade the content of seawater containing Direct Yellow 50 dye. The Experimental parameters such as initial dye concentration and time of reaction were assessed in a batch reactor to achieve the optimum operating circumstances. The Results of this study showed that more than 88% color removal was obtained after 35 min of O3 treatment (for 100 ppm dye concentration) and also partially removal of COD. These results also indicated that the application of O3 is more effective than UV assisted Ozonation to reduce the reaction time. Also, Gas Chromatography Mass Spectrum analysis of treated synthetic dye solution was performed at the end of the pre-treatment time to the final degradation products of Direct Yellow 50 dye and showed no toxic compounds.