In this paper, we report a one-step, high-yield synthesis of one-dimensional Ag heteronanostructures in aqueous solution. Besides the usual fcc: phase of Ag, the heteronanostructures also contain a rare hcp (4H polytypic) phase, which favors asymmetrical growth. The rod-needle heteronanostructures (RNHSs) and plate-belt heteronanostructures (PBHSs) are formed through two different mechanisms. For RNHSs, the 4H and fcc phases coexist but have different densities in different segments, white for PBHSs, the fcc: and 4H crystal structures exist in plate and belt segments, respectively. Condition-sensitive coexisting phase preferences can be applied as a new way of controlling the shape and thus the properties of Ag nanostructures.