A magneto-rheological fluid includes: a magnetic particle mixture; and a dispersion medium in which the magnetic particle mixture is dispersed. The magnetic particle mixture includes first magnetic particles and second magnetic particles. The first magnetic particles have an average particle size greater than or equal to 1 μm and less than or equal to 50 μm. The second magnetic particles have an average particle size greater than or equal to 20 nm and less than or equal to 200 nm, and have surfaces provided with a surface modified layer. A proportion of the second magnetic particles in the magnetic particle mixture is greater than or equal to 2 wt % and less than or equal to 10 wt %.