Abstract: <FONT face=Verdana>Nano-sized titania was prepared by hydrothermal synthesis in HCl medium using tetrabutyl titanate (TNB) as raw material.Product was characterized by X-ray diffraction (XRD).Effects of reaction conditions,such as reactant concentration,reaction temperature,and reaction time,on crystal phase composition and crystallite size of the product were investigated.Results showed that crystal phase composition was affected only by mix-ratio of the reactants (HCl/TNB).However,crystallite size was affected by both the reaction temperature and time.Result of photocatalytic degradation of methyl orange showed that the TiO<SUB>2</SUB> photocatalytic activity decreased with the decreasing of anatase ratio in the mixed crystallite of anatase,rutile,and brookite;and photocatalytic activity of pure rutile TiO<SUB>2</SUB> was relatively bad.</FONT>