[en] A new type of magnetic fluid was prepared by dispersing monodispersed iron-silica (Fe-SiO₂) composite particles in polyethylene glycol (PEG) 400. The composite particles Fe-SiO₂ were synthesized by hydrogen reduction from α-Fe₂O₃-SiO₂ spheres. Their microstructures were observed by a high-resolution transmission electron microscope (HRTEM) and the magnetism was characterized with a superconducting quantum interference device (SQUID) magnetometer. Both steady-state and dynamic rheological properties of the magnetic fluid under different magnetic fields were studied by using a rheometer. Experimental results show that this magnetic fluid has a relatively high magnetoviscous effect at low shear rates. The yield stress of this material shows an increasing trend with a magnetic flux density. Also, viscoealstic properties of such materials are different from conventional ones