Using titanium sulfate, Ti(SO4)2, as precursor and sodium hydroxide, NaOH, as adjusting reagent, pure brookite, pure anatase, and mixed-phase titanium dioxide (TiO2) with tunable brookite/anatase ratios were synthesized via a hydrothermal process. The samples were characterized by x-ray diffractionspectrometry, ultraviolet-visible diffuse reflectance spectrometry, transmission electron microscopy, and Brunauer-Emmett-Teller measurement. Photocatalytic degradation of Rhodamine B in aqueous solution served as a probe reaction to evaluate the photocatalytic activity of the as-prepared nanocomposites under visible irradiation (λ > 400 nm). The mixed-phase TiO2 exhibits higher photodegradation activity than single phase TiO2. The sample with 63.1% brookite and 36.9% anatase shows the highest degradation activity. Possible mechanism attributing to the enhanced activity was proposed based on the strucutre and surface property of the samples.