Abstract:Ultrafine Fe3O4 powder was synthesized by oxidation-precipitation technology with ferrous sulfate as raw material, sodium hydroxide as precipitating agent and air as oxidant. The effects of alkali ratio, synthesis temperature and oxidation rate on magnetic property of synthetic product were investigated. The results show that synthesized Fe3O4 powder has property of high coercive force and saturation magnetization under the optimum conditions including alkali ratio of 2.1~2.2, temperature of 80~90 ℃ and oxidation duration of 2~3 h. The morphology of magnetic powder has close relationship with magnetic property.