Gold nanoparticles（AuNPs） were electrodeposited onto the surface of a glassy carbon electrode（GCE）.The antibody of microcystin （leucine arginine）（anti-MC-LR） was immobilized on the film surface of AuNPs by the adsorption between Au nanoparticles and antibody.Non specific adsorption sites on the AuNPs were blocked with bovine serum albumin（BSA） to prepare an immunoelectrode anti-MC-LR/AuNPs/GCE.Microemulsion polymerization method was adopted to synthesize silica nanoparticles doped with tris（2,2′-bipyridyl） ruthenium（Ⅱ） complex ions（e.g.Ru@SiO2）.Ru@SiO2 nanoparticles and AuNPs on the surface of a GCE were characterized by transmission electron microscopy image（TEM） and scanning electron microscopy（SEM）,respectively.The Ru@SiO2 nanoparticles were further modified with amino groups by reacting with 3-aminopropyltriethoxysilane.The amino group modified Ru@SiO2 was then crosslinked with the carboxylic groups of microcystin （leucine-arginine）（MC-LR） by ethyl-3-（dimethyl aminopropyl） carbodiimide（EDC） and N-hydroxysuccinimide（NHS） to prepare Ru@SiO2-conjugated MC-LR（MC-LR-Ru@SiO2）.The immunosensor was based on the direct competitive immunoassay format between the labeled agent of MC-LR-Ru@SiO2 and the analyte.In the presence of MC-LR-Ru@SiO2,tripropylamine（TPA） was used as coreactant.MC-LR in solution was determined by electrochemiluminescence（ECL） method.The ECL intensity（I） decreases with the increase of MC-LR concentration after antigen-antibody reaction.A good linear relationship between the change of ECL intensity（ΔI） and the logarithm of MC-LR concentration was obtained in the range of 0.100-100 μg/L with a detection limit of 0.007 μg/L.The developed ECL immunosensor was used to determine MC-LR in real water samples with recoveries of 95.5%-105%.