The electrorheological (ER) properties of cellulose suspensions which include nonaqueous polar materials as active additives for ER effect were studied comparing with water‐activated suspension. The nonaqueous polar materials are alcohols, amides, and amines from the viewpoints of dielectric constant and vapor pressure. The ER properties of these suspensions were measured with a cylindrical rheometer at temperatures up to 120 °C. Also storage stability at 120 °C was investigated. The nonaqueous additives were effective to activate cellulose suspension: Especially at higher temperatures, the nonaqueous additives were more effective than water was. The shear stress of the water‐activated ER fluid decreased as the temperature increased. On the contrary the shear stress of the ER fluids, which contain the nonaqueous additives, increased as the temperature increased, and became greater than that of the water‐activated ER fluid at room temperature. Furthermore the nonaqueous additives had advantages of decreasing the electric power consumption and of improving thermal stability of shear stress after the storage for 250 h at 120 °C.