Electrorheological Behavior of suspensions using three different carbonaceous particles was observed from various characterization methods. These different carbonaceous particle possess different oxygen content and were prepared by thermal treatment. All were form mesophase pitch which were cationic polymerized with naphthalene and HF/BF under high temperature (500~700 ℃). Special attention was put on different variables effceting on ER properties such as current density, temperature, electric field and weight fraction. We also measured the change of shear stress and shear viscosity from 20 ℃ to 100 ℃ to observe the durability of carbonaceous ER fluid.