UV-Vis　spectroelectrochemistry　(SEC)　was　introduced　for　the　first　time　into　the　study　of　electrochemiluminescence　(ECL)　mechanisms　of　nitrogen　heterocyclic　compounds.　Uracil　and　its　two　derivatives,　5-fluorouracil　and　1-methyl-uracil,　were　chosen　as　model　molecules　in　the　ECL　mechanism　study.　SEC　revealed　that　the　substitution　of　hydrogen　at　N(1)　and　the　destruction　of　conjugate　heterocyclic　ring　were　very　important　for　ECL　activities　of　uracils.　On　the　basis,　a　new　ECL　mechanism　was　proposed　for　the　uracils.　The　successful　explanation　of　ECL　mechanism　for　the　model　molecules　by　employing　SEC　indicates　that　SEC　would　play　an　important　role　in　future　ECL　mechanism　studies.　(C)　2009　Elsevier　B.V.　All　rights　reserved.