Au nanoparticles prepared in ultrasonic field, were electrostatically assembled onto mica substrates treated with MnCl2 solution of certain concentration. Au nanoparticles were characterized by means of scan electron microscope (SEM), scan probe microscope (SPM) and X-ray diffraction (XRD). The results indicate that ultrasonic field distribution and power significantly influence the morphology of Au nanoparticles. Spindle Au nanoparticles were prepared in the standing wave field. The average aspect ratio decreases of the spindle Au nanoparticles with the ultrasonic power increasing. Monodispersed spherical Au nanoparticles were synthesized in the diffusion wave field. SEM and XRD results show that the average particle size is 25 nm. Au nanoparticals can self-assemble onto the mica surface with or without treatment, but they cover large areas on the treated mica