The device presented in the paper was used to study the propagation of heat in a magnetorheological suspension (MRS) based on mineral oil with stearic acid with iron micro-particles (mean diameter: 2.24 μm;standard deviation: 0.33 μm). The conclusion is reached that MRS can be assimilated to a semi-infinite medium. From the solution of the conductivity equation and limit conditions, the thermal conductivity of MRS was determined from the solution of the conductivity equation and boundary conditions. For MRS, with relative permeability μr=3, it is shown that in magnetic fields having intensities of up to H=100 kA/m, the thermal conductivity is influenced considerably by H, for well-defined values of the temperature in the fluid body.