A suspension (phi = 0.2) of Teflon particles in silicone oil exhibited a negative electrorheological response with a de electric field. This was in keeping with the fact that the conductivity of the host liquid sigma(f) was considerably greater than that of the particles sigma(p), giving for the complex dielectric mismatch parameter beta* = -1/2. Microscopy observations revealed that with application of a de electric field the Teflon particles migrated to the positive electrode resulting in Li structure which consisted of two layers or zones : (a) a relatively pure liquid and (b) a more concentrated suspension. The thickness of the liquid zone increased with field strength, which led to the decrease in the shear stress with field. A numerical analysis was developed for the electrical properties Of the segregated suspension, which gave good agreement with measured values.