The electrorheological properties (ER) of some fluids containing particles change extensively under the external electrical field. This phenomenon is applicable in many industries and equipments, such as clutches and motor driven rotor, which would transfer the spin to a drive shaft through a thin layer of electrorheological fluid. In this investigation, the effects of external electrical field on ER properties of non-Newtonian fluids (silicon oil) with the addition of SnO2 and Y2O3 nanoparticles were studied. The ER properties were measured for a wide range of SnO2 and Y2O3 nanoparticle concentrations and DC electrical voltages using concentric cylinder rotary rheometer. Based on the results, ER properties of nanofluids, e. g., apparent viscosity, shear stress, and yield stress, were enhanced by applying electrical field and increasing SnO2 and Y2O3 concentrations.