Abstract: Magnetorheological fluids with different densities were prepared using carbonyl iron and methyl-silicone oil as main raw materials.The relationship between density and saturation magnetization was studied and the rheologic behavior of the fluids with different densities was also investigated.The results show that the saturation magnetization was proportional to density of the fluid.When there was no external magnetic field,shear stress increased linearly with the increasing of shear rate but the viscosity decreased to a certain extent with the increasing of shear rate.The prepared fluids belonged to non-Newtonian fluid.The yield strength increased quickly with the increase of applied magnetic intensity.