A core-shell structure comprises a core (2) comprising nanoparticles and a shell (4) coating the core (2), and its void space (3) formed by the core (2) and the shell (4) is controlled. A method of preparing the core-shell structure comprises: forming particles comprising a photoetchable semiconductor, metal or polymer and coating the particles with a shell (4) comprising a non-photoetchable semiconductor, metal or polymer, to form a core-shell structure (5); and irradiating the core-shell structure with a light having a controlled wavelength in the photoetching solution to form an adjustable void space inside a shell (3) within the core-shell structure by the size-selective photoetching method. The core-shell structure allows the preparation of a catalyst exhibiting an extremely high efficiency, and can be used as a precursor for preparing a nanomaterial required for a nanodevice.