The photocatalytic oxidation of dichlorvos has been investigated with two different reactors. The reactor using 254 nm light is a system with TiO2 suspensions. The 360 nm light is used as the light source of the fixed system which was TiO2 coated on the inner surface of the reactor. In terms of quantum yield, the 254 nm radiation is more effective for dichlorvos oxidation than the 360 nm light. The effect of H2O2 on dichlorvos oxidation shows a negative performance. The influence of H2O2 on the photocatalytic oxidation of dichlorvos is greater in the fixed system than that in the suspension system. The ferrous ions can induce the photo-Fenton-type reaction. However, the photocatalytic oxidation of dichlorvos will be inhibited slightly at the concentration of 1.0 × 10−5 M Fe+2. This result is explained in terms of the net production of hydroxyl radical.