A series of siloxane-based liquid crystalline elastomers containing the smectic crosslinking agent M-1 and nematic monomer M-2 were synthesized by a one-step hydrosilication reaction. The chemical structures of the monomers and polymers obtained were confirmed by FTIR spectroscopy. The mesomorphic properties and phase behavior were investigated by differential scanning calorimetry (DSC), polarizing optical microscopy (POM), and X-ray diffraction (XRD) measurements. The influence of the crosslinking unit on the phase behavior was discussed. The experimental results demonstrated that the glass transition temperatures of elastomers had no remarkable change, and isotropization temperatures decrease with increasing the content of the crosslinking agent M-1. (C) 2004 Wiley Periodicals, Inc.