In this study, the apparent ozonation rate constants of 1:2 metal complex dyestuffs under different empirical conditions such as dye concentrations (400-1000 ppm), ozone-air flow rates (5-15 l min(-1)), the percentages Of 03 in the ozone-air flow rate (0.7-1.4), pH (3-12), temperatures (18-70 degrees C), powder activated carbon (PAC) (0.5-1.5 g in solution of 250 ml), HCO3- (0-26 mM) and H2O2 concentrations (0-21 mM) were determined. The ozonation of 1:2 metal complex dyestuffs was found to be fit pseudo-first-order reaction, and the apparent rate constants did not change with the increase of dyestuffs concentrations. For 1:2 metal complex dyestuffs, the apparent rate constants of dyestuffs degradation by ozonation increased with the augmentation of initial pH, H2O2, the percentage of O-3 in the ozone-air flow rate and PAC dosage in the solution, but decreased with the increase of HCO3-concentration and temperature of the solution. The apparent rate constant of dyestuffs degradation by ozonation increased with the augmentation of ozone-air flow rate from 5 to 10 l min(-1), but it did not change in the range of 10-15 l min(-1). At a high pH, the ozonation of 1:2 metal complex dyestuffs contributed to the increase the apparent rate constant due to the occurrence of hydroxyl free radicals. Using Arrhenius equation, the activation energy (E-a) of the reaction was found as 3 kJ mol(-1). The reaction of the ozonation of the dyestuffs under the different temperatures (291, 3 13 and 343 K) was defined as diffusion controlled according to E.,,. The model based on artificial neural network (ANN) could predict the concentrations of the dyestuffs removal from the aqueous solution during ozonation under the different conditions. A relationship between the predicted results of the designed ANN model and the experimental data was also conducted. The ANN model yielded 11 determination coefficient of R-2 = 0.978, a standard deviation ratio of 0.146, a mean absolute error of 19.503 and a root mean square error of 56.600. (C) 2007 Elsevier B.V. All rights reserved.