AbstractOzonation is a prospective method for the treatment of phenol‐contaminated wastewaters. In the present work, the reaction of ozone with 10 different substituted phenols was studied at acidic pH in two model gas–liquid contactors to investigate the dependency of the ozonation rate constant on the molecular structure of the phenolic compound. While three phenols were attached to electron‐donating functional groups, seven were characterized by the presence of electron‐accepting groups in their structure. In a stirred cell reactor (with flat‐cell interface) and mechanically agitated contactor, reaction kinetics for these two types of phenols were studied in the fast pseudo‐first order and chemical reaction controlled regime, correspondingly at T = 30°C. The effect of the electron‐donating or electron‐accepting functional group attached to the phenolic ring on the reactivity was studied and the linear dependence of the relative oxidation rate constant (with respect to phenol) on the Hammett substituent constant was proven in a Hammett plot. The values of susceptibility factor for the Hammett plots of phenols with electron‐donating and electron‐accepting substituents were −7.89 and −1.25, respectively. This work is useful to establish the ozonation pathway and predict the reaction rate constant from the molecular structure of the phenolic compound.