The　inclusion　of　methylmercury　(CH3Hg+)　in　the　environment　and　food　chain　has　aroused　wide　concern　due　to　its　high　neurotoxicity　and　cumulative　effects.　Herein,　a　highly　sensitive　electrochemical　sensor　based　on　manganese　dioxide　(MnO2)/gold　nanoparticles　(AuNPs)　composites　is　fabricated　for　CH3Hg+　detection　in　food.　The　MnO2/AuNPs　nanocomposites　were　synthesized　in　situ　on　the　surface　of　a　glassy　carbon　electrode　by　an　electrodeposition　method　and　were　characterized　by　scanning　electron　microscopy　(SEM),　energy　dispersive　X-ray　spectroscopy　(EDX),　cyclic　voltammetry　(CV),　and　electrochemical　impedance　spectroscopy　(EIS).　The　resulting　MnO2/AuNPs　modified　electrode　exhibited　a　large　active　surface　area,　enhanced　conductivity　and　excellent　electrocatalytic　activity　toward　CH3Hg+　due　to　the　synergistic　effect　of　MnO2　and　AuNPs.　Square　wave　anodic　stripping　voltammetry　(SWASV)　was　used　as　the　sensing　technique　for　CH3Hg+,　and　the　stripping　peak　current　showed　a　good　linear　relationship　with　CH3Hg+　concentration　in　the　range　of　0.7-15　μg　L−1　with　a　detection　limit　of　0.051　μg　L−1.　Besides,　the　interference　from　Hg2+　associated　with　CH3Hg+　detection　can　be　avoided　by　the　addition　of　diethylene　triamine　pentaacetic　acid　(DTPA).　The　as-prepared　sensor　was　applied　to　detect　CH3Hg+　in　various　food　samples　with　satisfactory　recoveries,　thus　providing　a　promising　platform　for　rapid　screening　of　methylmercury　residues.　©　2022　The　Royal　Society　of　Chemistry