In this work. the treatment of wastewater, containing azo dye reactive brilliant red X-3B using sequential ozonation and upflow biological aerated filter process has been studied. Decolorization was almost complete after 120 min with an ozone concentration of 34.08 mg/L, the biological oxygen demand for which was more 5 days (BOD5)/chemical oxygen demand (COD) ratio increased from 0.102 to 0.406, effective for the subsequent upflow biological aerated filter (UBAF) to reduce COD concentration. Under the conditions of gas/liquid = 3, hydraulic load = 4.8 m(3)/m(3).d, T = 20-25 degrees C, the mass ratio of ozone to dye = 4.5, pH 11, the COD and color of the effluent were less than 40 mg/Land 20 Pt-Co units, respectively, and the average decolorization and COD removal efficiency were 97% and 90%, respectively. The experimental results showed that the combination of ozone oxidation and upflow biological aerated filter was a promising technique to treat wastewater containing azo dye. (C) 2008 Elsevier B.V. All rights reserved.