An　electropolymerized　melatonin　modified　glassy　carbon　electrode　(EPMT/GCE)　was　prepared　by　electrochemically　polymerizing　of　melatonin　in　a　0.04　mol　l-1　perchloric　acid　solution.　In　KCl　solution,　Ca2+　was　found　to　perform　a　reversible　complex　reaction　on　the　EPMT/GCE　to　produce　a　sharp　complex　adsorption　wave.　The　configuration　of　the　electropolymerized　membrane　was　characterized　by　scanning　electron　microscope　and　various　electrochemical　techniques.　Based　on　which,　a　novel　sensitive　Ca2+　electrochemical　sensor　was　established.　The　peak　current　showed　a　linear　relationship　with　Ca2+　concentration　in　range　of　6.2　×　10-7-1.0　×　10-4　mol　l-1　with　detection　limit　of　4.5　×　10-7　mol　l-1.　The　developed　electrochemical　sensor　has　been　used　for　determination　of　Ca2+　in　body　fluid.　©　2008　Elsevier　B.V.　All　rights　reserved.