We report on the first experimental evidence of the electrorheological effect in suspensions of superfine pyrochlore-type Bi1.8Fe1.2SbO7 powders. Tensile-compressive and shear stress studies of the electrorheological fluids, with various filler contents, revealed an exceptionally high electrorheological effect in the materials - the tensile yield strength at 5 kV/mm reached about 20 kPa. The frequency dependencies of dielectric permittivity, dielectric loss tangent, and the conductivity of the suspensions with various filler contents allowed estimation of the dielectric permittivity values for superfine Bi1.8Fe1.2SbO7 particles at zero and infinite frequencies. The study reveals new oxide materials as promising fillers for electrorheological fluids. (C) 2019 Elsevier B.V. All rights reserved.