The present invention relates to an electrorheological semisolid capable of changing the rheological characteristics by an application of voltage. The semisolid is composed of 20-70 weight. Parts of carbonaceous particulates having an average particle size of 0.1-500 .mu.m and a carbon/hydrogen atomic ratio (C/H ratio) of 1.2-5 which are dispersed in 80-30 weight % of a dispersion medium comprising a partially crosslinked electric insulating polymer having a penetration of 40-475 at 25.degree. C., or into 80-30 weight % of a dispersion medium selected from an electric insulating oil having a viscosity of 5000 to 10.sup.9 centistokes at 25.degree. C. and an electric insulating polymer having a viscosity of 5000 to 10.sup.9 centistokes at 25.degree. C.