This work presents the degradation of five cytostatics found in Portuguese WWTP effluents: bicalutamide (BICA), capecitabine (CAP), cyclophosphamide (CYC), ifosfamide (IFO) and mycophenolic acid (MPA) using non-catalytic ozonation. Experiments were performed with 1 µM of each cytostatic at pH: 7.3 and room temperature (23 ºC). Tests in presence of t-BuOH demonstrated that CAP and MPA were quickly eliminated by direct ozonation, whereas BICA, CYC and IFO were more slowly degraded via hydroxyl radicals (HO•). Increasing the O3 dosage from 1 to 3 mgO3/mgDOC, CAP, MPA and IFO were completely removed, and BICA and CYC were converted to an extent higher than 90% after 3 h. Runs in river water and WWTP secondary effluent revealed that the presence of inorganic ions and organic matter did not affect the fast degradation of CAP and MPA. Nonetheless, there was an inefficient O3 usage, which resulted in only around 40% elimination of BICA, CYC and IFO after the same reaction time.