Magnetorheological polymer gels (MRPGs) are composite fluids containing ferrous particles suspended in a polymer gel. In addition to modification of the carrier fluid, the polymer gel, which includes crosslinked copolyimide (CCPI) and solvent N-octylpyrrolidone, also changes the surface properties of the ferrous particles, thus reducing the particle settling and improving particle redispersion. The viscosity of MRPGs can be easily adjusted by controlling the concentration of CCPI in the carrier medium. High thermally resistant CCPI is synthesized from dianhydride, diamine, diaminobenzonic acid, and crosslinker and has a high glass transition temperature because the crosslinking ratio can be controlled by the molar ratio of diamine to diammobenzonic acid. The redispersion and rheological properties are also investigated. (c) 2005 Wiley Periodicals, Inc.