This work reports the fabrication of double-tubular (or tube-in-tube) carbon nanofibers (CNFs). Tetra-layered nanofibers were manufactured using coaxial electrospinning with a concentric quadruple cylindrical nozzle system. Subsequent heat treatment eroded the first and third layers and converted the second and fourth layers into the carbonized structure, resulting in double-tubular CNFs. The morphologies and microstructures of the two tubes in the CNFs were investigated, revealing that the outer layer possessed denser and higher quality carbon crystals due to the coaxial electrospinning mechanism. Nanoparticles were readily incorporated between the two tubes in the double-tubular CNFs, providing a method for developing new multi-functional one dimensional materials.