The effect of hydrogen peroxide on the photocatalytic oxidation of phenol on illuminated TiO 2 has been investigated. The experimental results indicate that transition metal ions, such as Fe 3+ and Cu 2+, affect the photocatalytic oxidation of phenol. In the absence of added H 2O 2 the ferric ions induce the occurrence of the photo-Fenton-type reaction so that the phenol removal of an initial 1000 mg 1 −1 solution is enhanced from 23 to 33% within 8 h. However, the cupric ions show a negative effect. In the presence of added H 2O 2, both the ferric and the cupric ions enhance the phenol oxidation rate drastically. A 1000 mg 1 −1 phenol solution can be completely decomposed within 1 h and the total organic carbon removal reaches 80%. A reaction mechanism which involves the generation of hydroxyl radicals is proposed.