Abstract: Ag/polymethyl methacrylate(PMMA) nanocomposites were successfully in situ synthesized by ultrasonic radiating in the emulsion with methyl methacrylate monomers and silver salt but without initiator and reductant.The resultant Ag/PMMA nanocomposites were characterized by fourier transform infrared spectroscopy (FTIR),high resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD).The results show that the composites particles with nano-Ag as core showed good dispersion.The nano-Ag was polycrystalline and possessed high order of crystalline.