This paper presents the results of a study of a magnetorheological fluid (MRF) damper. The principle could be used for such applications as seismic protectors for civil structure (where the dimensions are chosen to handle the greatest forces) or shock absorbers for the automotive industry (where the dimensions are chosen to accommodate heating effects). We describe the preparation method and some characteristics of the MRF, the experimental method (we used a hydraulic linear motor and pressure measurements), and the main experimental results. The external force required to move the damper increases several times when the magnetic field is applied.