A novel complex-assisted hydrothermal route is presented to fabricate ultralong Ag/C nanocables with length ranging from 100 to 180 mu m on a large scale, based on the reaction of sulfamic acid silver and salicylic acid. By chemical etching of these Ag/C nanocables, high-quality carbonaceous nanotubes can be obtained at room temperature. Using the as-prepared Ag/C nanocables as templates, a new strategy for introducing guest materials into hollow nanotubes is addressed. We take Ag2Se as an example and validate the feasibility of this strategy. All of the products are characterized in detail by multiform techniques: X-ray diffraction, Fourier transform IR, energy-dispersive X-ray analysis, field emission scanning electron microscopy, transmission electron microscopy (TEM), and high-resolution TEM. The formation mechanisms of these products are tentatively proposed.