An understanding of the nucleation mechanism involved in the sonoelectrochemical synthesis of copper from sulfate bath is reported here. These explanations include the analysis of sono-chronoamperometric current transients and atomic force microscopy. The results indicate that ultrasound induces secondary nucleation by breakage of the existing primary nuclei in addition to the primary nucleation. The understanding of the sonoelectrochemical mechanisms clarifies a few unclear issues. It could possibly allow for the better design of sonoelectrochemical synthesis. (C) 2009 The Electrochemical Society. [DOI:10.1149/1.3243916] All rights reserved.