The　peroxidase-like　catalytic　activity　of　MoS2　nanomaterials　has　been　utilized　for　colorimetric　bioassays　and　medical　diagnostics.　However,　the　application　of　peroxidase-like　catalytic　activity　of　MoS2　nanomaterials　in　environmental　analysis　was　seldom　explored.　Herein,　copper　ions　were　found　to　inhibit　the　peroxidase-like　catalytic　activity　of　MoS2　nanosheets,　which　can　catalyze　the　oxidation　of　3,　3′,　5,　5′-tetramethylbenzidine　by　H2O2　to　produce　a　colorimetric　product.　Based　on　this　finding,　a　simple　sensitive　colorimetric　method　for　the　detection　of　copper　ions　was　developed.　In　the　presence　of　copper　ions,　the　absorbance　and　color　of　the　solution　decreased　with　the　increasing　concentration　of　copper　ions.　The　color　of　the　solution　can　be　used　to　semi-quantitative　on-site　assay　of　copper　ions　by　naked　eyes.　A　linear　relationship　between　the　absorbance　and　the　concentration　of　copper　ions　was　observed　in　the　range　of　0.4–4.0 μmol L− 1　with　a　detection　limit　of　92 nmol L− 1,　which　was　much　lower　than　the　maximum　contaminant　level　of　copper　in　drinking　water　legislated　by　the　Environmental　Protection　Agency　of　USA　and　the　World　Health　Organization.　The　method　was　applied　to　detect　copper　ions　in　environmental　water　samples　with　satisfactory　results.　©　2017　Elsevier　B.V.