Catkin, a natural hollow fiber, is used as a template to fabricate light, flexible, and electrically conductive silver microtubes with a high aspect ratio. The template is functionalized with tannic acid (TA)-Fe coordination complexes. Because of the metal ion chelating ability and reducibility of TA, silver nanoparticles (Ag NPs) can be formed in situ on the fiber's surface. The as-formed Ag NPs can act as nucleation sites in subsequent electroless silver plating, leading to the formation of a compact and uniform silver coating on the microtube. The coating is constructed by densely packed Ag NPs of only 15 ± 5 nm in diameter. Because of the tight accumulation and small size of the Ag NPs, the resulting silver-coated microtubes, without any post-treatment, show an electrical resistivity of 1500 mΩ·cm at a bulk density of 0.6 g·cm-3. We find that the in situ formed nucleation sites and the stirring speed in the electroless plating play important roles in the formation of a silver coating with a high electrical conductivity. This method may be extended to fabricate conductive nanocoatings on other substrates.