Nanocrystalline TiO2-diatomite composites (DT) were prepared by depositing TiO2 nanoparticles on the surface of diatomite microparticles. Thermal hydrolysis of titanium oxysulfate in aqueous suspension of diatomites led to the formation of uniform layer of TiO2 on diatomite. The degree of crystallinity of TiO2 nanoparticles was increased with thermal annealing as revealed by XRD analyses. SEM images of the composite samples show uniform layer of TiO2 is successfully deposited on diatomite surfaces. N-2 physical adsorption-desorption measurements show higher specific surface area of the composite sample compared to unsupported TiO2. The photocatalytic activity of the composite samples annealed at different temperatures was evaluated by the degradation of rhodamine B (RhB) dye in aqueous solution under UV-light irradiation and compared with the unsupported TiO2 powders. It is found that the photocatalytic reaction follow a pseudo-first-order rate law and the composite catalyst crystallized at 500 degrees C shows the highest catalytic activity toward RhB degradation. It was observed that diatomite substrate significantly enhanced the photodegradation efficiency of TiO2 due to higher surface area, mesoporous structure and uniform deposition of the small sized TiO2 particles. (C) 2014 Elsevier B.V. All rights reserved.