Pumice particles-based electrorheological (ER) suspensions were prepared in silicone oil and its ER behavior was investigated as a function of shear rate, electric field strength, concentration and temperature. Sedimentation stabilities of suspensions were determined. ER activity of all the suspensions was observed to increase with increasing electric field strength, concentration and decreasing shear rate. Yield stress of pumice suspensions increased linearly with increasing applied electric field strength and with concentrations of the particles. The pumice suspensions show a typical shear thinning non-Newtonian viscoelastic behavior, in which viscosity of suspension decreased sharply with increasing shear rate. Effect of high temperature onto ER activity of pumice/silicone oil system was also investigated.