A new kind of net‐like structure formed by the metal spheres suspended in a metal/oil electrorheological (ER) fluid is reported for the first time in this Letter. The experimental results show that this structure is totally different from that formed by dielectric particles. After comparing the two formation patterns, it is found that the dielectric particles in certain ER fluids align themselves into chains or columns in the direction of the external electric field. The metal particles in a metal/oil ER fluid, on the other hand, form a net‐like structure of chains and no column could be observed even when the ER fluid has been exposed to a high electric field. We attribute the net‐like structure of the metal ER fluid to the strong interaction between dipole fields induced on the metal particles under the external electric field. Finally, the dielectric properties of the different structures were measured and are discussed in this paper. ©1996 American Institute of Physics.