In the treatment of wastewaters contaminated with phenol and substituted phenols, an intermediate chemical step of partial oxidation is often employed to facilitate the ensuing biodegradation process. Ozonation is a candidate technique for partial oxidation of phenolics. In this study, the kinetics of ozonation reactions of 20 substituted phenols is investigated using the renowned theory of mass transfer with chemical reaction. The stirred (Lewis) cell with a flat interface is used as a model contactor. It is found that the second-order rate constants for the reactions with the chosen phenolic compounds are in the 10(4)-10(7) s(-1) range. In particular, the rate constant for ozonation of phenol is 5.06 x 10(6) M-1 s(-1). The liquid-side mass transfer coefficient is estimated by using the chemical method, and its value (k(L) = 0.052 cm s(-1)) is in line with those typical of stirred-cell reactors. This work is useful for the design, operation, and scale-up of ozonation reactors used in wastewater treatment.