Poly(p-phenylene) (PPP) particle-based electrorheological (ER) fluids were prepared from FeCl3-doped PPP and silicone oil. The effect of the volume fraction of PPP and applied electric field strength on ER response was investigated via measured rheological properties, including flow curve, shear viscosity, and yield stress. Furthermore, the yield stresses of the PPP-based ER fluid, which exhibit the typical characteristics of a Bingham fluid, were measured. The yield stress data collapse on a universal scaling function proposed by Choi et al.