Electrokinetic properties of Polythiophene-graft-Chitosan (PT-g-CS) copolymer were investigated by means of zeta (zeta)-potential measurements as a function of pH, electrolytes, surfactants, and temperature in aqueous medium. The c-Potential of pure PT was observed to enhance from +25 mV to +36 mV after grating with polycationic CS. Concomitantly, the isoelectric point of the pure PT shifted from 6.4 to 8.3. The zeta-Potential of PT-g-CS dispersion also shifted to more positive regions with increasing valency of the electrolytes and concentrations of cationic surfactant (cetyltrimethylammonium bromide). The c-Potential of PT-g-CS was determined to be +38 mV which indicated colloidal stability in silicone oil (SO) medium. Electrorheological (ER) and viscoelastic measurements revealed that the PT-g-CS/SO system has elasto-viscous behavior under applied electric field strengths. The yield stress of the ER fluid was determined to be a function of the electric field strength in a power law form as tau(y) = E-1.55 which obey to the conduction model. Creep and creep-recovery tests revealed reversible non-linear viscoelastic deformations of %31<%40<%43 under E=1; 2 and 3 kV/mm conditions. (C) 2016 Elsevier B.V. All rights reserved.