Water-soluble　carbon　nanocrystals　(CNCs)　with　electrochemiluminescence　(ECL)　activity　were　released　into　aqueous　solution　from　a　graphite　rod　by　applying　a　scanning　potential.　ECL　emission　of　CNCs　observed　during　their　preparation　probably　provides　a　useful　method　for　monitoring　and　screening　nanocrystal　preparation.　The　ECL　behavior　and　its　mechanism　in　CNCs　have　been　studied　in　detail　for　the　first　time.　The　results　suggest　promising　applications　of　CNCs　in　the　development　of　new　types　of　biosensors　and　display　devices　in　the　future　on　the　basis　of　their　strong　and　stable　ECL　emission,　good　stability,　low　cytotoxicity,　excellent　water　solubility,　easy　labeling,　and　environmental　friendliness.　©　2009　American　Chemical　Society.