Mesoporous metatitanic acid was prepared from industrial TiOSO 4 solution without using templates. Si-doped mesoporous SO 4 2– /TiO 2 with high thermal stability was then synthesized by impregnating mesoporous metatitanic acid with tetraethylorthosilicate solution and calcination. The calcined samples were characterized by X-ray diffraction, N 2 adsorption and desorption, scanning electron microscopy, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy. The photocatalytic activity of Si-doped SO 4 2– /TiO 2 for the degradation of methylene blue was tested. Tetraethylorthosilicate that was adsorbed in the pores of metatitanic acid formed Ti–O–Si bond by reaction with free –OH on the pore walls of metatitanic acid during calcination. Silicon atoms introduced into the framework of TiO 2 act as the pore structure support, and thus the thermal stability of mesoporous SO 4 2– /TiO 2 was improved. The sample calcined at 700 °C for 2 h had a surface area of 189 m 2 /g and an average pore diameter of 2.8 nm. The photocatalytic activity of the sample calcined at 400 °C was excellent.