Sliver doped n-type CdS nanoribbons (NRs) were successfully synthesized by using Ag2S as the dopant via a thermal co-evaporation method. The CdS:Ag NRs have wurtzite single-crystal structure with growth direction of [110]. Significantly, the conductivity of the CdS NRs increased ~6 orders of magnitude by silver doping. Moreover, the Ag doped CdS NRs showed much enhanced photoconductivity compared with the undoped ones, which will greatly favor the application of CdS nanostructures in high-performance nano-optoelectronic devices.