Naturally　oxide-covered　tantalum　electrodes　(Ta/Ta2O5)　are　first　used　in　the　determination　of　ultra-trace　catecholamines　based　on　hot　electron-induced　cathodic　electrochemiluminescence.　Under　natural　conditions,　an　oxide　film　can　be　formed　on　the　surface　of　tantalum　electrode,　at　which　the　quenching　effect　of　catecholamines　on　the　hot　electron-induced　cathodic　electrochemiluminescence　(cathodic　ECL)　of　luminol　is　found.　Based　on　this　quenching　effect,　detection　of　ultra-trace　catecholamines　is　established.　No　previous　anthropogenic　modification　of　the　electrode　and　no　derivatization　of　the　catecholamines　are　required　before　determination.　Under　the　optimum　conditions,　the　quench　ratio　is　linearly　increased　with　the　logarithm　of　the　concentration　of　epinephrine,　dopamine　and　norepinephrine　in　the　range　of　2.0　x　10(-8)　mol　L-1　to　2.0　x　10(-6)　mol　L-1,　8.0　x　10(-9)　mol　L-1　to　4.0　x　10(-7)　mol　L-1　and　8.0　x　10(-9)　mol　L-1　to　8.0　x　10(-7)　mol　L-1　with　the　limit　of　detection　(LOD)　of　5.5　x　10(-9)　mol　L-1　to　7.8　x10(-10)　mol　L-1　and　8.2　x　10(-10)　mol　L-1,　respectively.