Carbon–TiO₂ nanocomposites were fabricated by a simple hydrothermal process, and the content of carbon in the composites was adjusted by etching in air at high temperature. The synthesized nanocomposites were characterized by SEM, TEM, XRD, Raman, UV-vis spectroscopy and PL spectroscopy. The nanocomposites, with an average size of 50 nm, are composed of well-defined crystallized TiO₂ with the amorphous carbon either on the surface or among particles. And the TiO₂ are the mixed phase system of both anatase and rutile. Measurements of the photocatalytic degradation of rhodamine B show that the photocatalytic activity of the carbon–TiO₂ nanocomposites, especially after annealed at 400 °C, is higher than that of pure TiO₂. Experimental results indicate that the existence of the carbon enhances the photocatalytic activity of C–TiO₂ nanocomposites via the synergistic effect between carbon and TiO₂, such as improving the adsorption, retarding the recombination of photo-generated electron–hole pairs and absorbing more light.