Oxidation of an azo dye solution, namely, Acid Red 151 by the peroxone process was investigated experimentally at different pH values, initial dye and ozone concentrations, and the initial molar ratios (r) of hydrogen peroxide to ozone. At pH 2.5 in this process, the obtained color and chemical oxygen demand (COD) removals were higher than those at pH of 7 and 10. The best value of r yielding the highest treatment efficiency at each pH was determined as 0.5. The application of the "initial rates method" to the kinetic data for peroxone oxidation of aqueous Acid Red 151 solutions showed that the individual orders with respect to 03 and dye were one, the total order of the reaction being two. The rate constants based on the initial rates of dye degradation were determined as 98.9, 77.3 and 65.7 mM(-1) min(-1) at the pH values of 2.5, 7 and 10, respectively.