Disclosed are: Au—Ag core-shell nanorod particles wherein a cationic surfactant such as CTAB is substituted by an other compound and a method for producing the Au—Ag core-shell nanorod particles. Specifically disclosed are Au—Ag core-shell nanorod particles which are characterized in that each of the nanorod particles comprises a gold nanorod particle that serves as the core, a shell layer that covers the surface of the gold nanorod particle and is formed from silver, and a copolymer that adsorbs on the surface of the shell layer. The Au—Ag core-shell nanorod particles are also characterized in that the copolymer is a block copolymer or graft copolymer that is obtained by polymerizing at least a polymerizable monomer (A) that has a group represented by general formula (I). In the formula, Ra represents an alkylene group having 2-7 carbon atoms.