Fe3O4　nanoparticles　were　prepared　by　chemical　co-precipitation,　modified　with　dextran,　and　dispersed　in　water　to　form　a　magnetic　fluid　(MF)　for　use　in　biomedical　areas.　The　analyses　of　stability　and　magnetic　property　demonstrate　that　the　prepared　functional　MF　possesses　outstanding　stability　(stability　index　within　60　days,　high　dilution　stability,　and　autoclaved　stability)　and　high　magnetization　(the　values　chi　and　M-S　of　MF　are　5.87　x　10(-4)　and　20.57　emu/g,　respectively).　Due　to　the　coating　of　dextran,　the　toxicity　of　MF　is　minimal　(in　vitro　survival　rate　of　MCF-7　cells,　blood　compatibility,　and　in　vivo　toxicity).　In　addition,　although　the　outer　layer　is　coated　with　dextran,　the　MS　intensity　remains　high,　so　the　Fe3O4　MF　owns　a　fast　magnetic　temperature　response　(when　the　MF　concentration　is　55　mg/mL,　it　can　rapidly　rise　to　55　degrees　C　within　800　s),　which　plays　an　extremely　vital　role　in　MF　hyperthermia.　So,　the　MF　can　effectively　cause　necrosis　of　human　lung　A549　cells,　which　shows　a　certain　application　potential.