In this study. synthesis, characterization and electrorheological (ER) properties of polyindene (PIN) and polyindene/kaotinite composites were carried out by cationic radical polymerization using FeCl3 as the oxidizing agent. The homopolymer and composites, containing different amounts of PIN were characterized by FTIR spectroscopy, thermo-gravimetric (TGA) analyses, scanning electron microscopy (SEM) and dynamic light scattering (DLS) methods. The conductivity and dielectric properties of PIN and PIN/kaolinite composites were determined. Suspensions of PIN and PIN/kaolinite composites were prepared in silicone oil (SO), at a series of concentrations (c = 5-25 m/m %). The effects Of Concentration, shear rate, electric field strength, frequency, temperature and promoter on ER activities of suspensions were investigated.