Bi-disperse Electrorheological (ER) suspensions of two polarizable particles of the same size are investigated to understand the ER behavior of poly-disperse suspensions composed of various polarizable particles. The electrostatic polarization model is employed to describe ER suspensions, and solutions to the equation of motion are obtained by dynamic simulation. Even with the applied electric field, metastable structures and sheared configurations at a shear rate of 0.01 and 10 s^-1 show no inhomogeneous higher polarizable particle distributions (no higher polarizable particle cluster formation) regardless of the ratio of the two types of particles. The shear stress increases with the increase of the higher polarizable particle concentration both in the electrostatic farce and hydrodynamic force dominant regions.