The vibration properties of multi-layer beam structure comprising a partial magneto-rheologieal (MR) fluid layer are investigated to study the influences of size and location of the fluid treatment of the beam. The governing equations for the partially-treated multi-layered MR beam were formulated in the finite element form. The validity of the proposed finite element formulations is demonstrated by comparing the simulation results with those obtained from the Ritz formulation. Two different configurations of a partially treated MR-fluid beam are considered. Simulations are performed to investigate the influences of intensity of an external magnetic field, and the location and length of the MR-fluid layers on the dynamic characteristics of the beam with different boundary conditions. The properties and vibration responses of the partially-treated multi-layer beam are then compared with those of a fullytreated beam. The results suggest that the natural frequencies and transverse displacement response of the partially-treated MR beam are strongly influenced by the location and the length of the fluid pocket, and the boundary conditions, apart from the applied magnetic field. Copyright © 2010 by ASME.