The electrorheological (ER) behavior of suspensions in silicone oil of phosphated cellulose particles (average particle size 17.77 ${mu}{ extrm}{m}$) was investigated at room temperature with electric fields up to 2.5 KV/mm. In this paper, for development of anhydrous ER suspensions using at wide temperature range, we would like to know fundamental understandings on the ER activity. As a first step, the anhydrous ER suspensions dispersed the phosphated cellulose particles were measured, and not only the electrical characteristics such as dielectric constant, current density and electrical conductivity but also the rheological properties on strength of electric field and quantity of dispersed phase were studied. From the experimental results, the anhydrous ER suspensions dispersed phosphated cellulose particles showed a stable current density and very high performance of ER effect $( au/ au_0=1030)$ on the 2.5 KV/mm and the dynamic yield stress $( au_y)$ was in exponential proportion to the strength of electric fields.