Selective etching is significant for fabrication of novel nanostructures. Here silver ions are introduced to control the lateral etching of gold nanorods by K2PtCl4 in a hot solution, producing a number of dumbbell-like PtAu-Au thin gold nanorods. Silver ions control the selective deposition of the reduced Pt atoms, causing the selective etching of the unprotected Au. The middle diameter of the obtained dumbbell-like nanorods can be adjusted from 12 rim to <10 nm. It is believed that this is an effective method to reduce the diameter of gold nanorods.