Myriad　materials　with　desirable　functional　property　resulting　from　their　unique　structures　ignite　enormous　interest　in　synthesizing　materials　with　controlled　structural　morphology　toward　achieving　novel　or　enhanced　properties　for　target　applications.　Herein,　the　novel　and　unique　two-dimensional　(2D)　MoS2　nanosheet-coated　Bi2S3　discoids　composites,　which　feature　a　Bi2S3-core/MoS2-shell　structure,　have　been　elaborated　via　a　facile　anion-exchange　strategy.　Using　the　MoS2　nanosheets　to　coat　the　surface　of　Bi2S3　discoids　boosts　the　light-harvesting　efficiency　and　charge　separation　and　promotes　faster　charge　transport　and　collection,　thus　leading　to　the　higher　activity　of　the　photocatalytic　reduction　of　Cr(VI)　under　visible　light　irradiation　(λ　＞　400　nm).　In　particular,　the　phase　evolution　and　possible　formation　mechanism　of　the　MoS2-Bi2S3　core-shell　structure　have　been　explored　by　virtue　of　temperature-　and　time-dependent　experiments.　It　is　anticipated　that　this　work　could　promote　further　interest　in　adopting　an　anion-exchange　strategy　to　fabricate　semiconductor-based　composite　materials　with　controlled　architectural　morphology　and　enhanced　photocatalytic　performance　toward　diverse　applications.　©　2015　American　Chemical　Society.