In this study, electrorheological behavior of suspensions prepared from 0.9 and 5.0 mu m calcium carbonate particulates, dispersed in insulating silicone oil medium was investigated. Sedimentation stabilities of suspensions (c = 5 wt %) prepared using these calcium carbonate powders were determined to be 6 and 4 days, respectively. Electrorheological activity of all the suspensions was observed to increase with increasing electric field strength, concentration and decreasing shear rate. Shear stress of calcium carbonate suspensions increased linearly with increasing concentrations of the particles and with the applied electric field strength. Electric field viscosity of all the suspensions was decreased sharply with increasing shear rate and particle size, showing a typical shear thinning non-Newtonian visco-elastic behavior. Effects of elevated temperature and polar promoter onto electrorheological activity of calcium carbonate/silicone oil system were also investigated.