Objective:To evaluate the in vitro and in vivo toxicity of self-prepared nanosized Fe2 O3, which has the potential implication in tumor hyperthermia. Methods:Fe2O3 nanoparticles were prepared by improving co-precipitation, which characterization was detected by TEM, XRD, CMIAS, EDS. MTT assay was used to evaluate the in vitro cytotoxicity test; hemolytic test was carried out to estimate whether it has blood toxicity;Fe2O3 suspended in sterile 0.9% NaCl was intraperitoneally injected into Kunming mouse to calculate the LD50; micronucleus (MN) were reckoned to identify whether it is genotoxic. Results :The nanoparticles are brown spherical particles with diameter ranging from 8 to 15 nm, which have good decentralization and stability. The experiments also showed that the toxicity of the material on mouse fibroblast (L-929) cell lines was 0 - 1 degree; it has no hemolysis activity; LD50 arrived at 5.45 g/kg-1 after intraperitoneal injection of 1 ml suspension; micronucleus test showed that it has no genotoxic effects either. Conclusion:The results showed that the Fe2O3 nanoparticles are prepared successfully, the self-prepared nanosized Fe2O3 is a kind of high biocompatibility materials and perhaps it is suitable for further application in tumor hyperthermia.