This study’s relevance lies in the possibility of obtaining a smart sandwich structure with controllable dynamic properties, without compromising the main characteristics of conventional thin viscoelastic sandwiches. The proposed sandwich is composed of a micron-size viscoelastic-magnetorheological layer, which is obtained by adding spherical iron particles to a viscoelastic layer. Thin sandwiches with identical base layers and a viscoelastic core, with and without magnetic particles, are fabricated. Both the viscoelastic sandwich structure and viscoelastic-magnetorheological sandwich structure are experimentally characterised by a forced vibration test with resonance in a bandwidth between 0 and 1 kHz. This work analyses the influence of adding iron particles to obtain a smart thin sandwich. In addition, the vibrational response of the viscoelastic-magnetorheological sandwich structure under an external partial magnetic field, and the controllability of its dynamic properties by means of the magnetic field intensity and position, are studied.