In an electroviscous fluid comprising electrically insulating fluid as the dispersant and porous solid particles as the dispersed phase, at lease one substance selected from acid, salt and base and at least one substance selected from polyhydric alcohol and water, and further containing dispersing agent, antioxidant and/or corrosion inhibitor are added to obtain the better effects such as high responsiveness in wide temperature range up to high temperature, high reproducibility, excellent electroviscous effect and the higher durability.Therefore, the electroviscous fluid by this invention is useful, for example, for the control systems utilizing viscosity change, and it is capable to increase the control accuracy, particularly in the operation at high temperature.