Using ultrasonic technology, phenylmethylsilicone/organic montmorillonite (OMMT) nanocomposites were prepared by in-situ intercalative polymerization. The internal structure and morphology of nanocomposites were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM) analyses. The basal spacing of OMMT increases with the increasing of ultrasonic time. Intercalated and exfoliated phenylmethylsilicone/OMMT nanocomposites were successfully prepared by convenient process of changing ultrasonic time for 15 min and 30 min, respectively. The barrier property for water was obviously improved by adding OMMT into silicone. The water absorption rate of intercalated nanocomposite containing 4wt% OMMT is 0.7687%, which is 10 times less than that of pure silicone. However, the water absorption rate of exfoliated nanocomposite is 2.802%, which is 3 times less than that of pure silicone. The nanocomposite containing 6wt% OMMT has the best mechanical performance. The impact strength of intercalated nanocomposite is 1.593 2 kJ/m 2 , which is enhanced 7.45% more than that of pure silicone, and the impact strength of exfoliated nanocomposite is improved 14.4% to 1.695 7 kJ/m 2 . The tensile strength of intercalated nanocomposite was markedly enhanced from 1.247 MPa of pure silicone to 7.021 MPa and to 6.264 MPa for exfoliated nanocomposite. When nanocomposite contains 4wt% OMMT, the compressive strength of pure silicone is also evidently improved from 2.834 MPa to 10.232 MPa of intercalated nanocomposite and to 11.503 MPa of exfoliated nanocomposite, respectively. The hardness of exfoliated and intercalated PLS nanocomposites are both firstly increased with the increasing of OMMT content, and then decreased, and finally increased again.