Ozonation of 2-chlorophenol (2-CP), 4-chlorophenol (4-CP) and 2,4-dichlorophenol (2,4-DCP) in basic aqueous solutions is discussed. In such conditions (pH=9.5), ozonation of chlorophenols proceeds rapidly due to the presence of the dissociated form of the phenolic compound. No ozone occurs in the bulk of the liquid and, in modelling, it becomes necessary to account for the reactions in the liquid film. Two approaches were tested: 1) the film and bulk balances were solved sequentially, and the diffusional fluxes coupling the balances were obtained by solving numerically the concentration profiles in the film; 2) the bulk mass balances were solved without the film mass balances by applying the enhancement factor calculated from existing correlations. The results of both approaches are compared with experimental data. The formation mechanism of an aromatic quinone, hydrogen peroxide and chloride ions during the ozonation appeared to differ under basic conditions from that under acidic conditions. Hydroxyl radical reactions did not, however, have any effect on the chlorophenol decomposition.