Herein　we　design　a　sensitive　impedimetric　immunosensor　for　quantitative　detection　of　microcystin-LR　(MC-LR)　by　combining　antibody-conjugated　enzymatic　biocatalytic　precipitation　reaction　and　a　competitive　format.　MC-LR-bovine　serum　albumin　(MC-LR-BSA),　which　conjugated　onto　the　nanogold-modified　glassy　carbon　electrode　through　cysteamine　and　glutaraldehyde,　was　introduced　as　an　analyte　competitor.　Competitive　assays　were　performed　by　incubating　the　target　MC-LR　and　the　analyte　competitor　with　horseradish　peroxidase-labeled　monoclonal　anti-MC-LR　antibodies　(HRP-mAb).　After　the　competitive　reaction,　HRP　were　introduced　as　the　signal　labels　onto　the　immunosensor,　accelerating　the　biocatalytic　precipitation　reaction　of　substrate　4-chloro-1-naphthol　with　the　aid　of　H2O2.　The　enzymatically　generated　insoluble　precipitate　formed　an　insulting　layer　on　the　electrode　surface　and　efficiently　restricted　the　electron　transfer　of　redox　probe　Fe(CN)64-/3-,　resulting　in　an　enhanced　amplification　of　impedimetric　signal.　The　impedimetric　signal　decreased　with　the　increase　of　concentration　of　MC-LR,　and　exhibited　a　dynamic　linear　range　from　0.01　to　100　μg　L-1　with　a　detection　limit　of　0.004　μg　L-1.　The　proposed　immunosensing　method　can　be　applied　for　rapid　detection　of　MC-LR　in　real　water　samples　with　accuracy　comparable　to　the　high-performance　liquid　chromatography.　The　platform　shows　good　precision,　high　sensitivity　and　specificity,　which　opening　a　promising　horizon　for　monitoring　of　cyanobacterial　pollution　in　environmental　matrices.　©　2016　Elsevier　B.V.　All　rights　reserved.