The supersaturated solid-solution interfaces between Cu core and Ag shell structures improve their bonding strength and greatly prevent the outward diffusion of Cu atoms and slow down the growth of Cu oxides. The printed CuAg_x electrodes maintain high conductivity for a long time even at 220 °C, which is far better than the conventional Cu core/Ag shell and Cu/Ag mixed structures that rapidly oxidize below 150 °C. These findings not only promote the broad applications of Cu core/Ag shell structures but also pave a potential way for the fabrication of various stable core/shell structure materials.