Objective:To study the preparation and characterization of As2O3-loaded magnetic Fe3O4 albumin nanospheres which could be used in thermochemotherapy and reversing multidrug resistance of tumor. Methods:Fe3O4 magnetic nanoparticles were prepared by chemical co-precipitation method. Their characteristics were observed by transmission electron microscope (TEM),X-ray diffraction (XRD),and their cytotoxicity was measured by hemolytic test and MTT assay. As2O3-loaded magnetic Fe3O4 albumin nanospheres were prepared by desolvation-crosslinking method. Their characteristics were observed by TEM and energy dispersive spectrometer (EDS). Their hyperthermia induced by alternating magnetic field (AMF) was explored in vitro. The release rate of AS2O3 from the nanospheres was assessed by a dissolution test in vitro. Results:The prepared Fe3O4 magnetic nanoparticles were approximately spherical. The diameter was about 20 nm. They had no hemolysis activity and their cytotoxity was 1 class. The prepared As2O3-loaded magnetic Fe3O4 albumin nanospheres were approximately spherical,uniform in size observed by TEM. The diameter was about 193.4 nm. The temperature of magnetic fluid with different concentrations could rise to 39.5-58.0℃,and the magnetie fluid keep stable in AMF. The drug release test in vitro showed that As2O3-loaded magnetic Fe3O4 albumin nanospheres had a slow release rate. Conclusion:As a drug carrier,magnetic Fe3O4 nanoparticle is a kind of good biocompatibility material. The As2O3-loaded magnetic Fe3O4 albumin nanospheres can be prepared by desolvation-crosslinking method. They have an obvious effect of slow release of drug which may provide a theoretical and practical basis for further study of tumor thermochemotherapy and reversing multidrug resistance.