Abstract <p>The mechanism that generates clusters between rectangular electrodes in electrorheological (ER) fluids is analyzed through dielectric polarization. When the electric field is applied to ER fluids, positive charges appear on upper half surface of suspended particles, aligned in the direction of an electric field, while negative charges exist on their lower half surface in the opposite direction. The number of particles per chain is calculated by solving simultaneous equations of physical condition and geometrical condition. Consequently, the larger the dielectric mismatch value, the smaller the number of particles per chain. When a potential difference is applied between the electrodes, individual separation distances are maintained between neighboring particles without coming into direct contact with each other, unlike the case of disc electrodes and preserving equilibrium. Conversely, the number of chains is calculated by using Gauss’ law. As a result, the larger the dielectric mismatch value, the smaller the number of chains.</p> Graphical Abstract <p></p>