Mg-doped TiO2 with different Mg concentrations were prepared using sol-gel method and characterized by XRD, UV-visible, XPS, SEM and FT-IR. The XRD results revealed that Mg2+ goes into the TiO2 lattice. SEM images of the doped and pure TiO2 indicated that there is a smaller particle size for the doped catalyst compared to that of the pure TiO2. UV-visible absorption spectra indicated that upon doping with Mg2+ ion, the catalyst exhibits absorption in visible region. FT-IR and XPS spectra demonstrated that the presence of Mg2+ ion in the TiO2 lattice as substitutional dopant. Photocatalytic activity of doped TiO2 has been evaluated by degradation of the monocrotophos (MCP) pesticide. The effect of solution pH, catalyst dosage and initial concentration of MCP on the photocatalytic activity of Mg-doped TiO2 with different loadings was studied. It was observed that the rate of degradation of MCP over Mg-doped TiO2 is better than Pure TiO2 and Degussa P-25. (C) 2010 Elsevier B.V. All rights reserved.