Silver nanopartides with an atomically precise molecular formula [Ag-25(SR)(18)](-) (-SR: thiolate) are synthesized, and their single-crystal structure is determined. This synthesized nanocluster is the only silver nanoparticle that has a virtually identical analogue in gold, i.e., [Au-25(SR)(18)](-), in terms of number of metal atoms, ligand count, superatom electronic configuration, and atomic arrangement. Furthermore, both [Ag-25(SR)(18)](-) and its gold analogue share a number of features in their optical absorption spectra. This unprecedented molecular analogue in silver to mimic gold offers the first model nanoparticle platform to investigate the centuries-old problem of understanding the fundamental differences between silver and gold in terms of nobility, catalytic activity, and optical property.