We report a facile, single-crystalline Ag 2 Te nanorod formation based on electrochemical diffusion of Ag. The nanorods were grown non-epitaxially by sputtering deposition of GeTe on Ag 2 Te nanoparticles at room temperature. For the nanorod growth, the source of the Ag supply is not deposition but the diffusion of Ag from the nanoparticles. The growth of the single-crystalline Ag 2 Te nanorods required GeTe deposition onto Ag 2 Te nanoparticles, in contrast to the growth of amorphous Ag 2 Te nanorods caused by Te deposition onto Ag nanoparticles and the growth of other nanostructures caused by GeTe deposition on Ag nanoparticles. The GeTe deposition onto the Ag 2 Te nanoparticles of an amount equivalent to a 100-nm-thick film produced nanorods of a length ranging from 3 to 5 μm and a diameter ranging from 100 to 400 nm. We propose a model for the nanorod growth based on solid-state electrochemical reaction between GeTe and movable Ag ions, inducing nanoscale phase separation and precipitation of amorphous Ge. We suggest that the nanorod structure with a crystalline Ag 2 Te core and an amorphous Ge shell is useful for thermoelectric applications.