SYNOPSISWe have examined the rheological properties of a Co-adsorbed y-Fe203 magnetic suspension with polyurethane (PU) as a binder and methyl ethyl ketone (MEK) or cyclohexanone (CH) as a solvent. A Haake RV20 viscometer was used to measure the suspension viscosity and the vane method was adopted to determine the fluid yield stress. A rheological model which can be viewed as a combination of the Casson model and the Bingham model is proposed to describe the suspension viscosity. The effects of temperature, particle content, and binder concentration are included in the model.