In this study,silicone-oil-based γ-Fe2O3 magnetic fluid was successfully prepared by thermal oxidizing of Fe3O4 magnetic nanoparticles,which were prepared by chemical co-precipitation with FeSO4·7H2O and FeCl3· 6H2O,and their surface was modified by oleate ligands.Silicone oil was used as carrier liquid and oleic acid was as surfactant for preparing γ-Fe2O3 magnetic fluid.It is found that the Fe3O4 nanoparticles surrounded by oleate ligands are not damaged during the thermal oxidizing.The shape of γ-Fe2O3 magnetic nanoparticles prepared is similar to spherical,and their mean size is about 10-20 nm,which has nothing obvious difference compared with Fe3O4.The saturation magnetization of γ-Fe2O3 magnetic fluid prepared is 14.25 A·m2·kg-1 and that of γ-Fe2O3 nanoparticles is 57.56 A·m2·kg-1.The needle of γ-Fe2O3 magnetic fluid is much bigger than that of Fe3O4 magnetic fluid under the same magnetic field,which shows better magnetic properties.