The filling of multi-walled carbon nanotubes (MWNTs) with metallic silver nanowires via wet chemistry method was investigated. The carbon nanotubes were filled with long continuous silver nanowires. The carbon nanotubes were almost opened and cut after being treated with concentrated nitric acid. Silver nitrate solution filled carbon nanotubes by capillarity. Carbon nanotubes were filled with silver nanowires after calcinations by hydrogen. The diameters of silver nanowires were in the range of 20-40nm, and lengths of 100nm-10μm. We studied the micromorphology of the silver nanowires filled in carbon nanotubes by transmission electron microscopy (TEM) and X-ray diffraction (XRD). Based on the experimental results, a formation mechanism of the Ag nanowire-filled carbon nanotubes was proposed. And the microwave permittivity of the carbon nanotubes filled with metallic silver nanowires was measured in the frequency range from 2 GHz to 18 GHz. The loss tangent of the carbon nanotubes filled with metallic silver nanowires is high. So the carbon nanotubes filled with metallic silver nanowires would be a good candidate for microwave absorbent.