A　one-step　electrochemiluminescence　(ECL)　immunosensor　for　ultrasensitive　detection　of　carbohydrate　antigen　19-9　(CA19-9)　was　developed　based　on　multi-functionalized　graphene　oxide　(GO),　which　was　prepared　with　N-(4-aminobutyl)-N-ethylisoluminol　(ABEI)　and　CA19-9　antibody　(anti-CA19-9)　chemically　bound　to　the　surface　of　magnetic　GO　(nanoFe(3)O(4)@GO).　ABEI　and　anti-CA19-9　acted　as　the　electrochemiluminophore　and　the　capture　device　for　CA19-9　respectively.　NanoFe(3)O(4)@GO　enabled　all　the　ABEI　immobilized　molecules　electrochemically　active　due　to　its　good　conductivity,　and　brought　multifunctionalized　GO　attracted　on　the　surface　of　magnetic　glass　carbon　electrode　through　magnetism.　Thus　the　ECL　immunosensor　could　be　prepared　through　a　one-step　process　that　facilitates　ultrasensitive　detection　of　CA19-9.　Under　optimal　conditions,　the　ECL　intensity　of　the　immunosensor　decreased　proportionally　to　the　logarithmic　concentrations　of　CA19-9　in　the　range　of　0.001-5　U/mL　with　a　detection　limit　of　0.0005　U/mL.　This　one-step　ECL　immunosensor　showed　good　performance　in　specificity,　stability,　reproducibility,　regeneration　and　application.　It　opened　a　new　avenue　to　apply　multi-functionalized　bionanomaterials　in　ECL　immunoassay.　(C)　2014　Elsevier　B.V.　All　rights　reserved.