In this work, continuous ozonation of aqueous Acid Red-151 was performed in a stirred tank reactor at neutral pH and 25 degrees C. The results show that ozonation is capable of a rapid conversion of the Acid Red-151 dye molecule to more biodegradable intermediates up to the ozonation time of 120 min at which the optimum BOD5/COD ratio is obtained. The peak BOD5/COD ratios were found to be in the range of 0.028-0.35 for the initial dye concentrations being in the range of 1000-100 mg/L, respectively. The proposed kinetic modeling by Liakou et al. [S. Liakou, S. Pavlou, G. Lyberatos, Ozonation of azo dyes, Water Sci. Technol. 35 (4) (1997) 279-286; S. Liakou, M. Kornaros, G. Lyberatos, Pretreatment of azo dyes using ozone, Water Sci. Technol. 36 (2-3) (1997) 155-163] for another azo dye, namely Orange II, could be satisfactorily applied here, to the continuous ozonation of Acid Red-151, which allowed the prediction of the key variables measured experimentally, regardless of the particular intermediate compounds generated during ozonation. (c) 2005 Elsevier B.V. All rights reserved.