A　new　layered　compound,　Hg5AsS2I3,　has　been　synthesized　in　the　quaternary　system　mercury/arsenic/chalcogen/halogen　by　a　moderate-temperature　solid-state　reaction.　The　compound　crystallizes　in　the　space　group　C2/c　of　the　monoclinic　system,　and　its　structure　consists　of　(1)[Hg(1)(2)Hg(2)(2)As2/2S2]　eight-membered-ring　chains　bridged　by　Hg　atoms　to　form　[Hg(1)(2)Hg(2)(2)Hg(3)As2/2S2]　layers　with　inner-　and　interlayer　electrostatic　interactions　between　I　and　Hg.　The　optical　properties　were　investigated　by　means　of　diffuse　reflectance　and　FTIR　spectra.　The　electronic　band　structures,　along　with　density　of　states　(DOS)　calculations　by　DFT,　indicate　that　the　title　compound　is　a　semiconductor,　and　its　optical　absorption　mainly　leads　to　charge　transitions　from　I-5p,　As-4p　and　S-3p　states　to　Hg-6s　states,　and　both　I(1)　and　I(2)　atoms　contribute　to　the　top　of　the　valence　bands.