Oxidation of phenol and o- cresol by Chloramine- T has been investigated in acetic acid medium using Ostwald isolation method. The plots of log (a-x) versus time for [Chloramine- T] gave straight line graphs which shows the first order dependence of the reaction rate with respect to[ Chloramine- T]. The order of the reaction with respect to [ phenol/o- Cresol] is found to be zero. It is observed that as the acid strength increases the rate of oxidation of phenol as well as that of o- Cresol decreases. The effect of temperature has also been studied. The activation parameters calculated are summarized. The value of energy of activation is found to be more in the case of phenol which reveals that o- Cresol is more reactive towards Chloramine- T. From the results obtained a plausible mechanism is proposed.