A new class of materials termed MR elastomers (MRE) has been developed which responds to externally imposed magnetic fields. Magnetic particles are embedded in viscoelastic solids or liquid elastomeric precursors. This kind of composites demonstrates a unique combination of good magnetic controllability and elastic properties. A significant change in the structure of several MRE matrices was observed using AFM images. Morphological features such as interdomains of soft and hard segments of polyurethane elastomers were identified using AFM. The thermal and mechanical behavior was evaluated with a DMA and by DSC. This data demonstrated that the mechanical properties and thermal transition temperatures could be increased by increasing the hard segments. The glass transition temperature of polybutadiene-polyurethane is –75ºC and silicone has a lower glass transition at –106ºC. Polybutadiene - polyurethane – MRE with high stiffness can be obtained at optimum iron particle concentrations (60wt%) while maintaining good compressive force. Also, the stiffness is significantly increased under a magnetic field for oriented samples. Silicone / polybutadiene-polyurethane blend MREs have also been developed with good compatibility and excellent mechanical and thermal performance.