The viscosity change of micro magnetic particle immersed in a silicone oil has been characterized by an empirically driven mag- neto-rheological model. The viscosity increased with the particle volume fraction and the magnetic field and decreased with the shear rate and the temperature. An upper limit to the increase of viscosity by magnetic field was observed at B 80 mT and the effect of magnetic field was characterized by a sigmoidal type model. The effect of temperature and particle volume fraction was well described by the Arrhenius model and the Krieger amd Dougherty model. The multiplied form of magnetorheological model well represents the experimental data, and it can be very useful for the prediction of shear viscosity under various operating conditions