Abstract: Objective :To investigate the effects of epirubicin-carboxymethly dextran magnetic nanoparticles (EPI-CDMN) in combination with constant external magnetic fields on the proliferation and apoptosis of human bladder cancer cells in vitro. Methods : EPI-CDMN were prepared by the periodate oxidation-borohydride reduction procedure and its characters were detected. The human bladder cancer BIU-87 cells were divided into control group, magnetic fields group, epirubicin group, EPI-CDMN group, the group of EPI-CDMN combined with constant external magnetic fields. The growth inhibiting rate of BIU-87 cells was detected by the MTT technique, apoptosis of cells was observed by Annexin-V/PI double-labeled flow cytometry in vitro. Results : The diameter of EPI-CDMN was about 8～10 nm, the saturation magnetization was 0.22emu/g. The differences of growth inhibiting rate and apoptosis rate were not significant between EPI-CDMN group and epirubicin group(P>0.05). EPI-CDMN and constant magnetic fields could all inhibit proliferation of BIU-87 cells and induce apoptosis of cells. And the effects of EPI-CDMN on proliferation and apoptosis were significantly increased after coordination with constant external magnetic fields (P<0.01). Conclusion : EPI-CDMN in coordination with constant external magnetic fields can effectively kill human bladder cancer BIU-87 cells and can provided experimental basis for the magnetic targeting therapy of the tumor.