AbstractThree kinds of particles—polyaniline (PANI), poly(o‐toludine) (POT), and brominated polyaniline (Br‐PANI)—were synthesized. With chlorinated paraffin as a disperse oil, their electrorheological (ER) effects were determined so that the influence of the phenyl substitute group on the ER effects could be considered. POT exhibited the strongest ER effect, whereas the Br‐PANI ER effect was relatively poor. With the concept of polarization, this phenomenon was interpreted. The influence of the antidoping condition on the ER effects was also examined. An optimal antidoping condition was found for each kind of particle. Composite PANI/polyacrylamide (PAAm) and PANI/lithium polyacrylate (PAA‐Li) particles were further prepared by emulsion polymerization. The testing results showed that the composite particles with certain amounts of PAAm or PAA‐Li exhibited good ER effects. The dielectric and conductive behaviors were also determined so that the results could be explained. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 733–740, 2003