We　used　a　hydrothermal　method　to　prepare　In2S3　in　a　nanoform,　which　was　used　to　make　a　In2S3/g-C3N4　composite　photocatalyst.　The　obtained　photocatalysts　were　characterized　by　X-ray　diffraction,　scanning　electron　microscope,　and　transmission　electron　microscope　and　Fourier　transform　infrared　spectroscopy.　Photocurrent　response　analysis　showed　that　the　In2S3/g-C3N4　heterojunctions　had　higher　photocatalytic　activity　for　photodegradation　of　toluene　than　those　of　pure　In2S3　and　g-C3N4.　A　40%　loading　of　In2S3　on　g-C3N4　gave　the　highest　photocatalytic　degradation　activity　of　the　In2S3/g-C3N4　heterojunctions.　Here,　we　examine　the　photocatalytic　degradation　process　of　toluene　and　propose　a　plausible　photocatalytic　mechanism　©　2020　The　Authors