This paper, for the first time, reports on synthesis of Au@Pd core-shell nanoparticles in the absence of any capping and reducing agents by ultrafine bubbles and ultrasound. The mean diameter of the bimetallic core-shell nanoparticles was controlled by the ultrafine bubble concentration during the synthesis. The Pd shell thickness also varied with the concentration of Pd(II) ions. These Au@Pd core-shell nanoparticles showed excellent catalytic performance due to the pure surface without any capping and reducing agents.