Polyacrylonitrile (PAN)-based carbon nanofibers (CNFs) were prepared via the electrospinning process. Silver (Ag) modifications of these CNFs were carried out using in-situ Ag reaction as well as Ag coating methods. Ag modified CNFs from both methods yielded higher electrical conductivity than the neat CNFs due to the synergetic effect from the Ag nanoparticles. The effects of fiber diameter, fiber aspect ratio and the interconnecting network nature of the non-woven fiber mat on the electrical and thermal decompositional properties of as-prepared fibers were also investigated. The structural characterizations of as-prepared fibers were performed using SEM, Raman spectroscopy, WAXD, and TGA methods.