Three environment friendly beta-cyclodextrin polymer electrorheological (ER) particles (NS-beta-CDP, WSS-beta-CDP, and CLS-beta-CDP) were synthesized by copolymerization through a mixture of beta-cyclodextrin (beta-CD) and epichlorohydrin in the absence of starch or in the presence of water-soluble and water-insoluble starch, respectively. The electrorheological properties of suspensions in silicone oil were then investigated under direct current (dc) electric fields. It was found that the yield stress of the typical WSS-beta-CDP ER fluid was 6.2 kPa in 4 kV/mm, which is 35% higher than that of NS-beta-CDP and similar to that of CLS-beta-CDP. In the meantime, it can display a high ER performance even over a range of 65-95degreesC. The structures of these polymers were characterized by FT-IR and Raman spectrometry, respectively. The results demonstrated that all of these polymers keep the original structural character of beta-CD and the copolymerizations between starch and P beta-CD indeed occur. Furthermore, it was found that there was some relationship between the characteristic strength of polymers and their dielectric properties. Hence, the improvement of copolymer dielectric properties resulted in the enhancement of ER effects. (C) 2004 Wiley Periodicals, Inc.