Carbon　nanotubes　(CNTs)　have　been　developed　for　medical　and　biotechnological　applications　in　the　past　decades.　Their　widespread　applications　make　it　important　to　understand　their　potential　hazards　to　human　and　the　environment.　In　this　study,　the　possible　toxicological　effects　of　the　oxidized　multi-walled　carbon　nanotubes　(O-MWCNTs)　were　assessed　on　RAW　264.7　macrophages　in　vitro.　Several　toxicological　endpoints,　such　as　cell　viability,　the　release　of　LDH　and　IL-8,　GSH/GSSG　ratio,　intracellular　calcium　concentration　and　ultrastructural　changes　in　cell　morphology,　were　carried　out.　The　results　showed　that　O-MWCNTs　had　very　limited　effects　on　oxidative　stress,　cellular　toxicity　and　apoptosis.　Transmission　electron　microscope　clearly　demonstrates　RAW　264.7　macrophages　engulfed　plenty　of　O-MWCNTs,　and　some　of　them　resided　in　the　cytoplasm,　while　the　morphology　was　not　altered　by　O-MWCNTs.　As　the　control,　the　pristine　MWCNTs　(p-MWCNTs)　show　higher　cytotoxicity　than　O-MWCNTs,　damaging　cell　viability　and　inducing　cell　apoptosis.　All　these　toxicological　data　are　of　benefit　to　more　wide　applications　of　O-MWCNTs　in　the　future.