Oxidized　multi-walled　carbon　nanotube/nano-gold　(AuNP-ox-MWCNT)　composites　with　strong　electrochemiluminescence　(ECL)　activity　were　applied　to　construct　a　new　ECL　immunosensor　for　the　detection　of　carcinoembryonic　antigen　(CEA).　The　immunosensor　showed　a　linear　response　range　of　10-100　ng　mL−1　and　detection　limit　of　0.76　ng　mL−1　(at　a　signal-to-noise　ratio　of　3).　The　as-developed　immunosensor　exhibited　several　advantages,　including　being　simple　to　fabricate　and　being　label　free.　The　results　indicated　that　ox-MWCNTs　as　a　luminescent　material　have　great　application　potential　in　analysis.　©　2022　The　Royal　Society　of　Chemistry