In order to study an enhancement of TiO2 photocatalytic reaction efficiency by a prohibition of the recombination of photogenerated electron-hole pairs, a degradation of TOC of 4CP was carried out by using a photocatalytic-electrolysis reactor with an anode coated with a TiO2 thin film of anatase structure, a low surface resistivity, and a large surface area. At the photocatalytic anode under UV irradiation and with a potential to generate oxygen gas evolution being applied, the photocatalytic enhancement was about 90% because of taking out the generated electrons through an external bias into a cathode, and because of the oxygen generated by electrolysis reaction acting as an acceptor to the electrons. The photocatalytic enhancement effect occurred only when the cell voltage applied to the photocatalytic-electrolysis reactor was over a certain value. The photocatalytic reaction observed on the catalytic oxide electrodes of RuO2 and IrO2 was because of the existence of TiO2 on the electrode surface caused due to the oxidation of Ti substrate itself during sintering for the fabrication of the electrodes.