The degradation of the herbicide cyanazine in aqueous solution by ozone and UV radiation separately have been developed. In the ozonation process, the influence of the operating variables is observed, the stoichiometric ratio for the reaction is obtained, and a free radical reaction mechanism is proposed. The kinetic study establishes that the process is controlled by the chemical reaction, which takes place in the very slow kinetic regime. The reaction rate constants are determined as a function of temperature and pH. In the photochemical process, another mechanism is proposed and the disappearance rate equation is deduced. From a radiation source model, the radiation flow rate absorbed is evaluated. Finally, the reaction quantum yields are determined for different work temperatures.