Abstract: The giant electrorheological effect(GER) has been observed in a novel type of electrorheological suspension of coated nanoparticles that exhibits electrically controllable liquid-solid transitions in which the solid state can reach a yield strength more than 100 kPa, breaking the theoretical upper bound predicted by conventionally theoretical assumptions. This GER effect displays near-linear variation of the static yield stress versus the electric field, in contrast to the quadratic variation usually observed. A theoretical model, based on saturation surface polarization in the contact region of neighboring particles, yields predictions in excellent agreement with the experiment.