A silica nanofiber is derived from a crystalline polymer filament of a polymer including straight chain polyethyleneimine backbones, which is capable of forming a water-insoluble crystal in the presence of water molecules at room temperature, and the crystalline polymer filament in the silica concentrates metal ions, thereby realizing a composite nanofiber including metals or metal ions in the silica. Furthermore, the composite nanofiber of the present invention can be easily produced by fixing a polymer structure in the silica as the scaffold for metal ions and concentrating metal ions at the scaffold or reducing the metal ions. Furthermore, a metal-containing silica nanofiber can be easily obtained by removing a polymer component from the composite nanofiber, the composite nanofiber association, and the complex nanofiber structure. These nanofibers can be assembled and integrated, and the assembled or integrated association or structure can realize various shapes.