In this study, the vibration responses of a partially treated laminated composite magnetorheological (MR) fluid sandwich plate have been investigated. The governing differential equations of motion for a partially treated laminated sandwich plate embedding MR fluid and rubber as the core layer and the laminated composite plate as the face layers are presented in finite element formulation. The validity of the developed finite element formulation is demonstrated by comparing the results in terms of natural frequencies derived from the present finite element formulation with the experimental measurements. Various configurations of a partially treated laminated composite MR fluid sandwich plate are considered to study the effect of location and size of the MR fluid segment under various boundary conditions. The effect of magnetic field on the variation of natural frequencies and loss factor of the partially treated laminated composite MR fluid sandwich plate are also analyzed for various configurations at different boundary conditions. The free vibration mode shapes of various configurations of a partially treated laminated composite MR fluid sandwich plate are also presented. The forced vibration responses of the various configuration of a partially treated laminated composite MR fluid sandwich plate are also analyzed under harmonic force excitations. This analysis suggests that the natural frequency, loss factor and transverse displacements of the partially treated laminated composite MR fluid sandwich plate are strongly influenced by the location and size of the MR fluid segment apart from the intensities of the applied magnetic field. The application of the partial treatment alters the deflection pattern of the sandwich plate, particularly the location of peak deflection, which shows that it can be applied to critical components of a large structure to realize a more efficient and compact vibration control mechanism with variable damping. © The Author(s) 2014.