AgIn5S8　powders　were　successfully　synthesized　by　a　microwave　hydrothermal　method　for　the　first　time.　This　method　is　a　mild　and　highly　efficient　route　involves　no　templates,　catalysts,　or　surfactants.　Therefore,　it　is　very　promising　for　the　low-cost　and　large-scale　industrial　production.　The　samples　were　characterized　by　X-ray　diffraction,　UV-vis　spectroscopy,　X-ray　photoelectron　spectroscopy,　and　scanning　electron　microscopy.　The　photocatalytic　activity　of　AgIn5S8　nanoparticles　was　investigated　through　the　degradation　of　methyl　orange　under　visible　light　irradiation.　Compared　with　TiO2-xNx,　AgIn5S8　has　exhibited　a　superior　activity　under　the　same　condition.　A　liquid　chromatogram-mass　spectrometer　was　used　to　separate　and　identify　the　dye　and　degradation　products　generated　during　the　reaction.　According　to　the　experiment　results,　a　possible　mechanism　for　the　degradation　of　organic　pollutant　over　AgIn5S8　was　proposed.　(C)　2010　Elsevier　Inc.　All　rights　reserved.