In this study, functional pendants of chitosan were focused on enhancing the shear stress of electrorheological (ER) fluids. Chitosan succinates and chitosan phthalate were synthesized for ER particles and ER fluids were prepared by dispersing the particles in silicone oil. After comparing the shear stress of all prepared ER fluids, obtained conclusions were that ER particle having two functional groups (one is +ve charge and another is -ve charge) showed higher shear stress than that having only one functional group like the comparison between chitosan succinate(I) and chitosan succinate(II). However, though expect of the intermolecular overlapping between the rz electrons clouds supporting the charge carrier generation and transport leading to a significant delocalization of electrons, chitosan phthalate shows lower shear stress than chitosan succinate(I) and chitosan succinate(II). (c) 2006 Wiley Periodicals, Inc.