Three kinds of polymer/layered nanocomposites were prepared via ultrasonic extrusion. Experimental results showed that ultrasonic oscillations could mostly decrease the size and its distribution of clay particles in polymer matrix. Therefore, crystal size of polymer matrix decreases. For PA6-based nanocomposites with higher compatibility, the ultrasonic oscillations can also affect the microstructure of clay, causing more regions of exfoliated clay. Due to better dispersion of clay and smaller crystal size, the elongation at break of polymer/layered nanocomposites ultrasonically treated got greatly increased, meanwhile ultrasonic oscillations also improved their other mechanical properties, such as tensile and impact strength.