ABSTRACTA titanium-boron binary oxide has been prepared by the sol-gel method and characterized using SEM, TEM, UV-VIS reflectance, and X-ray diffraction spectroscopies. These measurements indicated that the obtained Ti/B gel with no treatment exhibited an amorphous structure. After calcination in O2, the crystalline structure of titanium oxide species in the Ti/B binary oxide was changed while boron oxide species maintained in the state of amorphous. Titanium oxide species in the Ti/B binary oxide calcined at 673 K showed an anatase phase of TiO2, and changed with the calcination temperatures from anatase phase to rutile phase. The Pt loaded Ti/B photocatalysts in aqueous suspension system decomposed water stoichiometrically under UV-irradiation. Their photocatalytic activities decreased with increasing the calcination temperature, indicating the photocatalytic activities of the Ti/B binary oxides were depended on the crystal phase of titanium oxide in the Ti/B photocatalysts.