According to physical and chemical designs, a novel modified kaolinite/carboxymethyl starch (CMS) nanocomposite was synthesized with a displacement method with dimethyl sulfoxide modified kaolinite as an intermediate. The material characterizations were carried out by X-ray diffraction, transmission electron microscopy, thermogravimetric analysis, and scanning electron microscopy. The analyses showed that kaolinite was dispersed at the nanometer-scale segments into the CMS matrix. The electrorheological behavior of the modified kaolinite/CMS hybrid nanocomposite dispersed in silicone oil was investigated. Under electric field strength (E) = 4 kV/mm and shear rate (((gamma) over dot)) = 105 s(-1), the shear stress of the modified kaolinite/CMS nanocomposite electrorheological fluid could be up to 8380 Pa, which was 10.4 times that of the electrorheological fluid at zero field. The modified kaolinite/CMS nanocomposite electrorheological fluid also exhibited good sedimentation properties. (C) 2008 Wiley Periodicals, Inc.