Noble metal nanoparticles with hollow interiors and customizable shell compositions have immense potential for a wide variety of applications. Herein, we present a facile, general, and cost-effective strategy for the synthesis of noble metal nanoparticles with hollow structures, which is based on the inside-out diffusion of Ag in solid-state core-shell nanoparticles. This approach starts with the preparation of core-shell nanoparticles with Ag residing in the core region, which are then loaded on a solid substrate and aged in air to allow the inside-out diffusion of Ag from the core region, leading to the formation of monometallic or alloy noble metal nanoparticles with a hollow interior. The synthesis was carried out at room temperature and could be achieved on different solid substrates. In particular, the inside-out diffusion of Ag calls for specific concern with respect to the evaluation of the catalytic performance of the Ag-based core-shell nanoparticles since it may potentially interfere with the physical and chemical properties of the core-shell particles.