In this study, the performance of a new controllable mount design utilizing a magnetorheological material encapsulated in an elastomer matrix is investigated. A magnetorheological fluid-elastomer (MRF-E) mount is designed and fabricated, and its dynamic performance is studied under harmonic oscillatory vibrations for a wide range of frequencies and various applied magnetic fields. Also, a theoretical analysis is conducted by proposing a three-element phenomenological model for replicating the dynamic behavior of the MRF-E mount under oscillation loadings, and the results are compared with the experimental data. In order to further evaluate the effectiveness of the MRF-E mount for vibration control, a single degree-of-freedom (SDOF) system incorporated with this device is developed. Theoretically, the equation of motion utilizing the proposed phenomenological model is derived to provide performance predictions on the effectiveness of the semiactive device at suppressing unwanted vibrations. Experimentally, a SDOF system constrained to rectilinear motion and composed of a mass, four linear springs, and the MRF-E mount is designed and manufactured. This work demonstrates the performance of the proposed MRF-E mount and its capability in attenuating undesirable system vibrations for a range of small-displacement amplitudes and frequencies.