Electro-Mechanical Spinning (EMS) technology has evolved from electrospinning to achieve greater deposition control of individual nanofibers. This paper aims to investigate the morphology change of electro-mechanically spun suspended carbon nanofibers as a function of the increase of the applied current passing through the fiber and the attendant Joule heating leading to the sublimation of the fibers. Controlled sublimation potentially can be developed into a technique for thinning nanofibers. Present work details two studies – Joule heating of the suspended fibers in a vacuum and in the ambient environment. It is concluded that due to the differences in thermal dissipation mechanisms, fibers heated in vacuum are sublimated more uniformly than the fibers heated up in the ambient environment. Theoretical evaluation confirms that temperatures required for sublimation of the glassy carbon fibers can be achieved during Joule heating at the specified materials properties, geometry of the fibers, and the observed current levels.