Kinetics of oxidation of cetirizine hydrochloride using potassium dichromate as oxidizing agent in acid medium was studied spectrophotometrically at 520 nm. The result interprets that rate of oxidation is first order with respect to potassium dichromate and cetirizine hydrochloride where as it does not depend on the concentration of acid. The stoichiometry of the reaction was found that one mole of oxidant is consumed for oxidation of three moles of cetirizine hydrochloride and the product found is cetirizine N-oxide. From the results of kinetic studies, reaction stoichiometry and product analysis with suitable mechanism of the reaction was proposed. Based on results of the reaction at different temperatures, the activation parameters with respect to the slow step of the proposed mechanism were calculated.