In this study, decolorization of three disperse dyes by ozonation was evaluated. The dyes assessed represent low (CI Disperse Blue 56), medium (CI Disperse Blue 60) and high (CI Disperse Blue 79) energy level dyes. UV-visible spectroscopy, HPLC-DAD and COD analysis were performed to follow the removal of color from effluent. The results indicated that color removal rates up to 100% and COD removal rates up to 68% could be achieved via ozonation. HPLC analysis and UV-vis analysis were performed for all of the dyes, and a degradation mechanism was proposed for CI Disperse Blue 79.