Silicon nanowires (SiNWs) with tens of micrometer in length have been synthesized and modified with Ag nanoparticles, which were confirmed by X-ray diffractometer (XRD), scanning electron microscopy and transmission electron microscopy. The Ag/Si nanostructure was employed to detect inorganic ions SO2-4 via surface-enhanced Raman scattering (SERS) with strong signals at low concentrations of 1
10-9 mol/L. This ultrasensitive method might be applied in other fields.