Abstract: Magnetic fluids were prepared by chemical precipitation method with water as a based liquid.The technical process and properties of a series of prepared magnetic fluids were studied.The dispersing properties of nanosized Fe3O4 in water and magnetic particle size were analyzed by scanning electron microscopy (SEM).The composed phases of magnetic particles were identified by X-ray diffraction (XRD).The saturated magnetization intensity of the magnetic fluid was measured by vibrating sample magnetometer.The size of the magnetic particles of the aqueous magnetic fluids were between 10nm and 20nm by choosing an ideal surfactant.The saturated magnetization intensity was up to 15.51Gs.The coercivity and remanence were almost zero.