Composite mesoporous TiO2/MCM-41 photocatalysts was prepared via a sol–gel method using an activated MCM-41 mesoporous molecular sieve as carrier. The morphology and photocatalytic activity of TiO2/MCM-41 photocatalysts were characterised by the X-ray diffraction, Brunauer–Emmett–Teller, Fourier transform infrared and TEM spectra, and the degradation experiment of Acid Red B aqueous solution was also investigated. The results showed that the TiO2 nanocrystalline could firmly combine with MCM-41 by Ti–O–Si. The results also showed that the samples were calcined at 600 °C for 2 h, and the prepared 30 wt-%TiO2/MCM-41 photocatalysts possessed highest photocatalytic activity with a clearer mesoporous structure and larger specific surface area. Furthermore, the composite mesoporous TiO2/MCM-41 photocatalysts exhibited excellent performance in the degradation of Acid Red B aqueous solution under ultraviolet irradiation, and the prepared photocatalysts were stable and could be recycled without considering loss of activity.