In this study, CdS nanowires (NWs)/Ag nanoparticle materials (CdS@Ag) with Schottky junction were synthesized by a simple process. The Ag nanoparticles with a diameter of 3-10 nm were uniformly scattered on the surface of CdS NWs with an average diameter of 30 nm. The gas sensing properties and the effect of Ag content and relative humidity on the ethanol sensing properties of CdS NWs were investigated in detail. When the relative humidity was below 60% RH, the sensor, especially the one based on CdS@Ag0.1, exhibited an enhanced ethanol sensing response and selectivity compared with that of pristine CdS NWs, which was believed that Ag catalyzed the reaction between ionized oxygen species and ethanol. However, excessive Ag content does not mean a higher response and even decreased the response. Also, the stability of CdS NWs and CdS@Ag NWs was also investigated, which were almost stable for four months.