The effects of additive metal ions on photo-catalytic oxidation of phenol in aqueous solution was studied on a bench scale using TiO2 and UV as the PCO system. It was considered that ferric ion (Fe3+) and ceric ion (Ce4+) could increase the efficiency of degradation of phenol in PCO reaction, only if Fe3+ and Ce4+, as electron acceptors, could prevent the recombination of hole-electron in the surface of TiO2. From the quantitative investigation, it was found that ferric ion increased the efficiency of degradation of aqueous phenol during PCO reaction, with concentration range of [Fe3+] = 0.1～0.3 mM. Especially, in case of 0.2 mM of ferric ion, the reaction time for the complete destruction of aqueous phenol decreased to 1/3 of the control case (i.e. 150 min → 50 min). However, ceric ion (Ce4+) was rarely effective with concentration range of [Ce4+] = 0.02 mM, but, still showed the possibility of electron acceptors.