The effect of titanium oxides with various crystalline structures in the photo-decomposition of phenolic contaminants in aqueous solutions was studied. The structural types of titanium oxide under investigation varied from anatase and rutile phases of TiO2 (either commercially available or laboratory-made) to layered and pillared titanates. The photodegradation of several phenolic compounds was examined, such as phenol, 4-chlorophenol, 2,3,5-trichlorophenol and 2,4,6-trichlorophenol. The activities of the catalysts of various structures were compared based on the same titanium content as 0.01 g TiO2 suspended in 50 ml of aqueous solution containing 1.25 mM phenolic compounds, with an O-2 gas flux of 10 ml/min as oxidant and illumination with 300 nm UV radiation. The results showed that laboratory-made TiO2 either in the anatase or rutile phase gave better catalytic activity than the commercially available materials when catalysts were properly pretreated. The high activity of the as-prepared lab-made rutile was attributed to the large amount of hydroxy groups present on the catalyst surface, which might stabilize electron-hole pairs. On the other hand, layered titanates, whose charged surface might contribute to the destabilization of electron-hole pairs as well as strong adsorption of phenolic intermediates, showed low photocatalytic activity.