Ozone decomposition into free radicals, which can be facilitated by enhancing electron transfer between ozone and catalyst, is an important segment in catalytic ozonation. We doped cerium uniformly on γ-Al2O3 with an impregnation–calcination method to enhance electron transfer in catalytic ozonation of phenol in aqueous solution. The removal efficiency of phenol is raised from 39.7% by ozonation alone to 46.3% by catalytic ozonation with Ce/Al2O3 in 50 min reaction. A higher Ce3+/Ce4+ ratio in Ce/Al2O3 witnesses a higher electron transfer rate in catalytic ozonation and thus a higher degradation efficiency of phenol, illustrating that the activity of Ce/Al2O3 depends on the valence state of Ce. The electron transfer cycle is formed by the electron donation from Ce3+ to ozone molecule and the electron acceptance of Ce4+ from adjacent lattice oxygen. After getting the electron, the ozone molecule is decomposed to generate free radical of ·OH on the surface of Ce/Al2O3. The continuous flow experiments exhibit a stable and high catalytic activity of Ce/Al2O3 for catalytic ozonation, implying the feasibility in practical application.