UV irradiation of highly dispersed, anchored titanium oxide catalyst and finely powdered TiO 2 catalysts in the presence of a mixture of CO 2 and H 2 O led to the formation of (CH 4 + CH 3 OH + CO) and CH 4 , respectively, into the gas phase at 275 K. The efficiency of these photoreactions depended strongly on the kind of catalyst, the ratio of CO 2 to H 2 O, and the reaction temperature. In the case of highly dispersed titanium oxide catalysts, the charge transfer excited state, i.e. (Ti 3+ O − ) 3* of the tetrahedral coordinated titanium oxide species was found to play an important role in the appearance of a highly efficient reactivity. The anatase-type TiO 2 catalyst with large band gap and numerous surface OH groups showed high efficiency for the formation of CH 4 . Detection of Ti 3+ , H, C and CH 3 radicals by electron spin resonance at 77 K suggests that the photoreaction of CO 2 with H 2 O proceeds via the formation of CO and C radicals from CO 2 . The Cu-loading on the small powdered TiO 2 catalyst brought about new formation of CH 3 OH, and the Cu + species on TiO 2 were found to play a significant role in this photocatalytic reaction. In the case of single crystals of rutile TiO 2 , the surface of TiO 2 (100) exhibited a higher efficiency for the formation of CH 4 and CH 3 OH than TiO 2 (110). Measurements of the intermediate species formed on the TiO 2 (100) single crystal were carried out using high resolution electron energy loss spectroscopy.