Au nanoring@Ag core-shell nanostructures with controllable morphologies and tunable symmetries are synthesized via the seed-mediated growth of Ag onto a sole seed: a circular Au nanoring (AuNR). The 2D isotropic AuNR is prepared firstly by chemical etching, then by galvanic replacement with HAuCl4. By delicately altering the regrowth procedure and mixing the capping agents, different Ag triangular nanoplates with embedded AuNRs in different sizes and shapes can be obtained. Furthermore, by using a single capping agent, the growth of Ag on the AuNR can be preferentially confined to a lateral or vertical mode, to form eccentric nanoplates or nanocubes in both sequence sets at room temperature. Such nanostructures with precisely controllable shape evolution not only displayed unique optical properties, but also revealed the feasibility of breaking the original dimensions, and especially symmetry, at the nanoscale using seed-mediated growth. This paves the way for future applications including catalysis, diagnosis, plasmonics, and biological and chemical sensing.