Electrorheological (ER) fluids are generally composed of electrically polarizable inorganic or organic particles dispersed in insulating oils. These materials are intelligent/smart materials in that they are capable of changing their state from liquid-like to solid-like very quickly under an applied electric field. This feature article reviews the literature regarding the fabrication of conducting polyaniline (PANI) and PANI composite particles, their ER performance, as well as their chemical and physical characteristics of morphology and crystal structure. The ER behavior of these intelligent materials was also analyzed using a range of rheological equations of state and their dielectric properties.