The activities of various titanium oxide containing compounds in photocatalytic decomposition of phenol were compared. The structures of titanium oxide under investigation varied from crystalline anatase and rutile TiO2 phases, layered titanates, small titanium oxide crystallites pillared in between the clay interlayers, to titanium/silicon mixed oxides prepared by either coprecipitation or impregnation. The activities were compared based on the catalysts having the same Ti content as 0.01 g TiO2, suspended in 50 ml of 0.01 M phenol in the presence of an oxygen flux of 10 ml/min flow-rate and illuminated with 300 nm UV radiation. The photocatalytic activity as well as the photoluminescence intensity were found to be strongly influenced by the structure of titanium oxide. Of the catalysts which were studied, anatase and titanium oxide impregnated over silica gel were the most active photocatalysts with regard to the degradation rate of phenol, while carbon dioxide formation was fastest over the latter catalyst. Coke formation was proposed to be a result of strong interaction between charged surfaces and phenolic intermediates, and accounted for the low activities of layered and pillared titanates, pillared clays as well as rutile. The particle size quantization effect of titanium oxide was found to play only a small role in the catalytic activities.