Cyclophosphamide is a hazardous cytostatic drug, which should be removed from wastewaters before disposals. Ozonation slowly inactivates this substance, requiring long reaction times to obtain degradation. In this paper, different advanced oxidation processes (AOPs) are studied for cyclophosphamide oxidative degradation in aqueous medium: ozone at several basic pH values, ozone/hydrogen peroxide at neutral and basic pHs with the addition of the peroxide at the beginning of ozonation. The influence of ozone concentration in the gas phase and gas flow is also discussed. Results show that, under the experimental conditions studied, the radical mechanism acting in the AOPs rapidly degrades cyclophosphamide. Additionally, second‐order rate constants k_d and k_OH were determined for direct (molecular) and indirect (radical) reactions. Finally, reactions were carried out with the aim of isolating and identifying some of the degradation products. From ozonation at pH 9, 4‐ketocyclophosphamide was identified as the main reaction product.