This paper describes the synthesis of Pd−Au bimetallic nanocrystals with controlled morphologies via a one-step seeded-growth method. Two different reducing agents, namely, l-ascorbic acid and citric acid, were utilized for the reduction of HAuCl₄ in an aqueous solution to control the overgrowth of Au on cubic Pd seeds. When l-ascorbic acid was used as the reducing agent, conformal overgrowth of Au on the Pd nanocubes led to the formation of Pd−Au nanocrystals with a core−shell structure. On the contrary, localized overgrowth of Au was observed when citric acid was used as the reducing agent, producing Pd−Au bimetallic dimers. Through this morphological control, we were able to tune the localized surface plasmon resonance peaks of Pd−Au bimetallic nanostructures in the visible region.