A monoclinic structure SrBi2O4 was prepared by coprecipitation method and characterized using X-ray diffraction (XRD), scanning electron microscope (SEM) and diffuse reflection UV-vis spectra (DRS). Photocatalytic activity of the catalysts was evaluated through the degradation of acetaldehyde and Escherichia coli (E. coli) under visible light irradiation (lambda > 420 nm). The results indicated that monoclinic structure SrBi2O4 shows visible light activity and its photocatalytic activity was greatly enhanced when further loaded with NiO by the impregnation method. This is attributed to NiO promoting the electron-hole separation and interfacial charge transfer. The FT-IR spectra of the used NiO/SrBi2O4 indicated that some intermediates such as acetic acid, H2O, CO2 were formed for the degradation of acetaldehyde. The determination of intracellular K+ leakage with the inactivation of E. coli verified that the outer membrane of the cell is destroyed, causing the cell to die under visible light excitation of NiO/ SrBi2O4. ESR studies revealed that center dot OH, O-2(center dot-) were involved as the active species in the photocatalytic reaction. A possible visible light photocatalytic mechanism was proposed. (c) 2006 Elsevier B.V. All rights reserved.