Semiconductive polyaniline and its derivatives such as poly(aniline-co-sodium diphenylamine sulfonate), poly(aniline-co-ethoxyaniline), poly(o-methylaniline), and poly(o-methoxyaniline) were synthesized, and then adopted as suspending particles of the electrorheological (ER) fluids. All suspensions of these polyaniline derivatives showed typical ER properties under high applied electric fields. However, flow behaviors are observed to be quite different depending on the polyaniline derivatives, especially in the stress plateau regions obtained at low shear rates. Using a scaling law, we also obtained universal curves of ER fluids from the flow curves at each applied electric field based on the relationship between the dynamic yield stress with the applied electric field and flow curve changes according to the electric fields.