In the present work, we have developed a novel route to synthesize metal nanorods and nanofibers capped by polymer shells, which can be called the reverse micelle-gas antisolvent-ultrasound method. Using this method, we have successfully synthesized Ag core/polystyrene (PS) shell composite nanorods and nanofibers. By changing the ultrasound procedure, PS fibers with discrete embedded Ag particles were formed. The Ag/PS nanocomposites were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), UV-vis spectra, X-ray photoelectron spectra (XPS), and FT-IR spectra. The effects of the experimental conditions on the final morphologies of the composite particles were studied. The results show that the length of the composite nanorods is increased with increasing ultrasound time, while the shell thickness depends on the polymer molecular weight.