In　this　work,　a　new　colorimetric　biosensor　for　the　assay　of　paraoxon　was　developed　via　the　conventional　iodine-starch　color　reaction　and　multi-enzyme　cascade　catalytic　reactions.　In　the　presence　of　acetylcholine　chloride,　acetylcholinesterase　(AChE)　and　choline　oxidase　(ChO)　catalyzed　the　formation　of　H2O2,　which　then　activated　horseradish　peroxidase　(HRP)　to　catalyze　the　oxidation　of　KI　to　produce　an　iodinestarch　color　reaction.　Upon　exposure　to　paraoxon,　the　catalytic　activity　of　AChE　was　inhibited　and　less　H2O2　generated,　resulting　in　a　decrease　in　the　production　of　I-2　and　a　drop　in　the　intensity　of　solution　color.　This　colorimetric　biosensor　showed　high　sensitivity　for　the　assay　of　paraoxon　with　a　limit　of　detection　4.7　ppb　and　was　applied　for　the　assay　of　paraoxon　in　spiked　real　samples.　By　employing　the　conventional　iodine-starch　color　reaction,　this　biosensor　has　the　potential　of　on-site　assay　of　OPs　residues　in　environmental　samples.　(C)　2017　Elsevier　B.　V.　All　rights　reserved.