A label-free self-enhanced electrochemiluminescence（ECL） immunosensor was fabricated for the ultrasensitive detection of tetrodotoxin（TTX） based on immobilizing tris（2,2′-bipyridyl） ruthenium（Ⅱ）-Au nanoparticles（Ru（bpy）2+3-AuNPs） composites to glassy carbon electrode（GCE） with Nafion.In this strategy,an anti-TTX was able to fix on the electrode surface via Au-N chemical bond for realizing the specific capture toward the target.Meanwhile,TTX could be used as the co-reactant of Ru（bpy）2+3 to promote the ECL intensity.The advantage of this approach is that the electron transfer distance between the emitter and the co reactant is shorter,and the ECL efficiency is improved and the experimental cost is reduced compared with that in the presence of co-reactant in solution or labeling of second antibody.Under the optimum conditions,the change of ECL intensity demonstrated a linear relationship with TTX concentration in the range of 0.01-1 000 μg·L-1,with a limit of detection（LOD） down to 0.01 μg·L-1.This label-free self-enhanced ECL immunosensor exhibited an excellent performance with good stability,reproducibility and sensitivity.The recoveries for TTX in real samples were in the range of 98.0%-104.0%,indicated it has good practical value.