Abstract: The photo catalytic reduction of Cr 6+ ions on a novel immobilized photo catalyst(TiO 2)is studied. Oxygen produced by the photo catalytic reduction was measured. The mechanism of photo catalytic reduction of Cr 6+ ions was verified by detecting the change of dissolved oxygen of the solution. The effects of pH values on the rate of the reaction were investigated: the higher pH results in lower reduction rate. The experimental results show that some organic compounds also have influence on the reduction reaction: methanol and acetic acid accelerate the process, while chloroform, pentane and toluene restrain it. The deposition of Cr(OH) 3 on the surface of photo catalyst will result in the deactivation of the photo catalyst. The deactivated photo catalyst can be partially regenerated by immersing it in diluted acidic solution.