Abstract: This invention pertains to electroviscous fluids comprising a dispersion in an electrical insulating fluid of microparticles that are comprised of a polyelectrolyte or a mixture of a polyether and a polyelectrolyte wherein said polyelectrolyte consists of a carboxyaryl group-containing organopolysiloxane that has been neutralized by a base containing a monovalent or divalent metal. The electroviscous fluids of this invention provide a high electroviscous effect and good dispersion stability, and they are thermally stable and do not abrade surrounding equipment.