Coreshell　Fe3O4@Au　magnetic　nanoparticles　(NPs)　were　modified　onto　the　surface　of　the　screen-printed　working　electrode,　and　the　antibody　of　microcystin-(leucine-arginine)　(anti-MCLR)　was　immobilized　on　the　film　surface　of　Fe3O4@Au　NPs　by　the　adsorption　between　Au　nanoparticles　and　antibody.　Subsequently,　bovine　serum　albumin　(BSA)　was　used　to　block　the　non-specific　adsorption　sites　of　the　electrode　to　obtain　immunosensor　for　the　detection　of　MCLR.　The　immunosensor　was　based　on　the　direct　competitive　immunoassay　format　between　the　labeled　agent　of　horseradish　peroxidase-conjugated　MCLR　(MCLR-HRP)　and　the　analyte.　MCLR　was　determined　by　differential　pulse　voltammetry　(DPV).　Under　the　optimal　experimental　conditions,　the　peak　current　response　decreased　proportionally　with　the　concentration　of　MCLR　in　the　range　of　0.79-12.9　mu　g　L-1　with　a　detection　limit　of　0.38　mu　g　L-1.　The　developed　biosensor　was　used　to　determine　MCLR　in　real　water　samples　with　the　recoveries　of　standard　additions　of　95%　107%.　The　proposed　immunosensor　possesses　the　properties　of　fast,　sensitive　and　portable,　etc.