The ability of Ce-containing bioactive glasses, based on 45S5 Bioglass (R), to inhibit oxidative stress in terms of reduction in hydrogen peroxide and superoxide (O-2 (-)), by mimicking the catalase and superoxide dismutase activity is reported in this work. The characterization is performed on the powders of pristine glasses and after the soaking in H2O2 solutions and simulated body fluid. The glass samples are analysed by XPS, XRD, UV-Vis and FT-IR. The best catalyst activities are obtained for the glass with the highest content of cerium (H_5.3 = 5.3 mol% of CeO2 in the nominal glass composition), and the best Ce3+/Ce4+ ratio in terms of catalase mimetic activity is found to be a function of H2O2 concentration. Moreover, the detailed study of the surface during the mimic enzymatic activity tests shows the formation of a Ca-P-rich layer on the glass surface, where the presence of Ce ions favours the formation of CePO4. The phosphate in turn inhibits the formation of hydroxyapatite, decreasing the bioactivity of the glass with the highest of CeO2 in the glass composition. This work shows the effect of Ce3+/Ce4+ ratio towards the catalase mimetic activity and for the first time the superoxide dismutase mimetic activity of Ce-containing 45S5-derived glasses.